v3.26.3
Average Annual Total Returns
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LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   17.72% 13.16%     12.41%                                       9.32%
Performance Inception Date Jun. 14, 1996                                                  
LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   9.20% 8.57%     8.21%                                       7.21%
LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   15.20% 9.43%     8.79%                                       7.31%
LARGE CAP FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                                       10.18%
LARGE CAP FUND | Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.37% 13.59%     14.59%                                       10.34%
LARGE CAP DISCIPLINED EQUITY FUND | SIIT LARGE CAP DISCIPLINED EQUITY FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   17.54% 14.88%     13.49%                                   10.12%    
Performance Inception Date Aug. 28, 2003                                                  
LARGE CAP DISCIPLINED EQUITY FUND | SIIT LARGE CAP DISCIPLINED EQUITY FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   13.07% 10.37%     9.30%                                   7.49%    
LARGE CAP DISCIPLINED EQUITY FUND | SIIT LARGE CAP DISCIPLINED EQUITY FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   12.30% 10.43%     9.44%                                   7.50%    
LARGE CAP DISCIPLINED EQUITY FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                                   11.07%    
LARGE CAP INDEX FUND | SIIT LARGE CAP INDEX FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   17.22% 13.52%     14.53%                                     9.90%  
Performance Inception Date Apr. 01, 2002                                                  
LARGE CAP INDEX FUND | SIIT LARGE CAP INDEX FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   13.16% 10.05%     11.56%                                     8.26%  
LARGE CAP INDEX FUND | SIIT LARGE CAP INDEX FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   12.63% 10.04%     11.20%                                     8.00%  
LARGE CAP INDEX FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                                     9.88%  
LARGE CAP INDEX FUND | Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.37% 13.59%     14.59%                                     9.95%  
S&P 500 INDEX FUND | SIIT S&P 500 Index Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   17.81% 14.35%     14.75%       13.63%                                
Performance Inception Date Dec. 18, 2013                                                  
S&P 500 INDEX FUND | SIIT S&P 500 Index Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   14.69% 11.21%     12.69%       11.83%                                
S&P 500 INDEX FUND | SIIT S&P 500 Index Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   12.60% 10.90%     11.89%       11.09%                                
S&P 500 INDEX FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%       13.69%                                
EXTENDED MARKET INDEX FUND | SIIT Extended Market Index Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   12.55% 6.71%     11.45%         11.25%                              
Performance Inception Date Feb. 28, 2013                                                  
EXTENDED MARKET INDEX FUND | SIIT Extended Market Index Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   9.71% 4.30%     9.50%         9.46%                              
EXTENDED MARKET INDEX FUND | SIIT Extended Market Index Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   9.16% 4.82%     8.93%         8.88%                              
EXTENDED MARKET INDEX FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%         14.51%                              
EXTENDED MARKET INDEX FUND | Russell Small Cap Completeness Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell Small Cap Completeness Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   12.67% 6.69%     11.40%         11.22%                              
SMALL CAP FUND | SIIT SMALL CAP FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   9.79% 8.26%     9.12%                                       8.29%
Performance Inception Date Jun. 14, 1996                                                  
SMALL CAP FUND | SIIT SMALL CAP FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   3.86% 4.69%     5.98%                                       6.29%
SMALL CAP FUND | SIIT SMALL CAP FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   9.47% 5.70%     6.47%                                       6.34%
SMALL CAP FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                                       10.18%
SMALL CAP FUND | Russell 2000 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 2000 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   12.81% 6.09%     9.62%                                       8.24%
SMALL CAP II FUND | SIIT Small Cap II Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   12.90% 8.54%     10.21%             10.62%                          
Performance Inception Date Apr. 10, 2012                                                  
SMALL CAP II FUND | SIIT Small Cap II Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   10.32% 5.51%     7.48%             7.90%                          
SMALL CAP II FUND | SIIT Small Cap II Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   9.21% 5.89%     7.39%             7.78%                          
SMALL CAP II FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%             14.58%                          
SMALL CAP II FUND | Russell 2000 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 2000 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   12.81% 6.09%     9.62%             10.25%                          
SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   3.68% 6.35%     8.50%                                 8.26%      
Performance Inception Date Dec. 15, 2003                                                  
SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   1.90% 3.63%     5.75%                                 6.06%      
SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   3.45% 4.46%     6.11%                                 6.20%      
SMALL/MID CAP EQUITY FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                                 10.89%      
SMALL/MID CAP EQUITY FUND | Russell 2500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 2500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   11.91% 7.26%     10.40%                                 9.50%      
U.S. EQUITY FACTOR ALLOCATION FUND | SIIT U.S. Equity Factor Allocation Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   17.99% 15.18% 14.16%                                            
Performance Inception Date Apr. 26, 2018                                                  
U.S. EQUITY FACTOR ALLOCATION FUND | SIIT U.S. Equity Factor Allocation Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   16.26% 12.23% 12.06%                                            
U.S. EQUITY FACTOR ALLOCATION FUND | SIIT U.S. Equity Factor Allocation Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   11.48% 11.18% 10.91%                                            
U.S. EQUITY FACTOR ALLOCATION FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42% 14.91%                                            
U.S. EQUITY FACTOR ALLOCATION FUND | Russell 3000 Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 3000 Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.15% 13.15% 14.18%                                            
U.S. MANAGED VOLATILITY FUND | SIIT U.S. Managed Volatility Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   10.75% 10.02%     9.66%                     11.61%                  
Performance Inception Date Dec. 31, 2008                                                  
U.S. MANAGED VOLATILITY FUND | SIIT U.S. Managed Volatility Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   (3.06%) 4.22%     5.60%                     8.11%                  
U.S. MANAGED VOLATILITY FUND | SIIT U.S. Managed Volatility Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   14.86% 7.14%     7.06%                     8.85%                  
U.S. MANAGED VOLATILITY FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                     14.81%                  
U.S. MANAGED VOLATILITY FUND | MSCI USA Minimum Volatility Index (Net) (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI USA Minimum Volatility Index (Net) (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.31% 8.01%     9.92%                     11.55%                  
U.S. MANAGED VOLATILITY FUND | Russell 3000 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Russell 3000 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.15% 13.15%     14.29%                     14.58%                  
U.S. MANAGED VOLATILITY FUND | The Fund’s 75/25 Blended Benchmark Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] The Fund’s 75/25 Blended Benchmark Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   9.81% 9.28%     10.62%                     12.15%                  
GLOBAL MANAGED VOLATILITY FUND | SIIT Global Managed Volatility Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   17.90% 11.20%   9.78%                                          
Performance Inception Date Jan. 29, 2016                                                  
GLOBAL MANAGED VOLATILITY FUND | SIIT Global Managed Volatility Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   14.01% 7.92%   7.44%                                          
GLOBAL MANAGED VOLATILITY FUND | SIIT Global Managed Volatility Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   12.92% 8.07%   7.28%                                          
GLOBAL MANAGED VOLATILITY FUND | MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                  
Average Annual Return, Percent   32.39% 7.91%   9.26%                                          
GLOBAL MANAGED VOLATILITY FUND | MSCI World Index Return (reflects no deduction for fees or expenses)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI World Index Return (reflects no deduction for fees or expenses)                                                  
Average Annual Return, Percent   21.09% 12.15%   12.97%                                          
GLOBAL MANAGED VOLATILITY FUND | MSCI World Minimum Volatility Index (USD) Return (reflects no deduction for fees or expenses)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI World Minimum Volatility Index (USD) Return (reflects no deduction for fees or expenses)                                                  
Average Annual Return, Percent   10.54% 6.29%   8.04%                                          
WORLD EQUITY EX-US FUND | SIIT WORLD EQUITY EX-US FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   29.32% 7.73%     8.81%                             6.11%          
Performance Inception Date Mar. 28, 2005                                                  
WORLD EQUITY EX-US FUND | SIIT WORLD EQUITY EX-US FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   25.67% 5.48%     7.32%                             5.05%          
WORLD EQUITY EX-US FUND | SIIT WORLD EQUITY EX-US FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   19.70% 5.68%     6.89%                             4.83%          
WORLD EQUITY EX-US FUND | MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                  
Average Annual Return, Percent   32.39% 7.91%     8.41%                             6.21%          
SCREENED WORLD EQUITY EX-US FUND | SIIT Screened World Equity Ex-US Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   27.87% 8.06%     10.00%                       5.39%                
Performance Inception Date Jun. 30, 2008                                                  
SCREENED WORLD EQUITY EX-US FUND | SIIT Screened World Equity Ex-US Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   22.30% 5.53%     8.44%                       4.45%                
SCREENED WORLD EQUITY EX-US FUND | SIIT Screened World Equity Ex-US Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   19.42% 5.88%     7.95%                       4.28%                
SCREENED WORLD EQUITY EX-US FUND | MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                  
Average Annual Return, Percent   32.39% 7.91%     8.41%                       4.75%                
EMERGING MARKETS EQUITY FUND | SIIT EMERGING MARKETS EQUITY FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   39.81% 9.20%     10.14%   7.29%                                    
Performance Inception Date Oct. 31, 2014                                                  
EMERGING MARKETS EQUITY FUND | SIIT EMERGING MARKETS EQUITY FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   31.12% 6.40%     8.20%   5.55%                                    
EMERGING MARKETS EQUITY FUND | SIIT EMERGING MARKETS EQUITY FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   28.57% 6.89%     7.93%   5.54%                                    
EMERGING MARKETS EQUITY FUND | MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI All Country World Ex-US Net Index Return (reflects no deduction for fees or expenses)                                                  
Average Annual Return, Percent   32.39% 7.91%     8.41%   6.66%                                    
EMERGING MARKETS EQUITY FUND | MSCI Emerging & Frontier Markets Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] MSCI Emerging & Frontier Markets Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   33.78% 4.26%     8.39%   5.38%                                    
OPPORTUNISTIC INCOME FUND | SIIT Opportunistic Income Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   6.15% 5.09%     4.38%                         2.35%              
Performance Inception Date Dec. 14, 2006                                                  
OPPORTUNISTIC INCOME FUND | SIIT Opportunistic Income Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   3.61% 2.86%     2.53%                         0.95%              
OPPORTUNISTIC INCOME FUND | SIIT Opportunistic Income Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   3.60% 2.92%     2.54%                         1.16%              
OPPORTUNISTIC INCOME FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%                         3.17%              
OPPORTUNISTIC INCOME FUND | ICE BofA USD 3-Month Deposit Offered Rate Constant Maturity Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] ICE BofA USD 3-Month Deposit Offered Rate Constant Maturity Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   4.42% 3.26%     2.38%                         1.89%              
CORE FIXED INCOME FUND | SIIT CORE FIXED INCOME - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   7.54% (0.30%)     2.45%                                       4.83%
Performance Inception Date Jun. 14, 1996                                                  
CORE FIXED INCOME FUND | SIIT CORE FIXED INCOME - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   5.71% (1.68%)     0.91%                                       2.84%
CORE FIXED INCOME FUND | SIIT CORE FIXED INCOME - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   4.44% (0.83%)     1.22%                                       2.94%
CORE FIXED INCOME FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%                                       4.37%
HIGH YIELD BOND FUND | SIIT HIGH YIELD BOND FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   7.96% 5.63%     7.02%                           7.03%            
Performance Inception Date Dec. 05, 2005                                                  
HIGH YIELD BOND FUND | SIIT HIGH YIELD BOND FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   4.16% 1.69%     3.42%                           3.55%            
HIGH YIELD BOND FUND | SIIT HIGH YIELD BOND FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   4.64% 2.52%     3.78%                           3.87%            
HIGH YIELD BOND FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%                           3.30%            
HIGH YIELD BOND FUND | ICE BofA U.S. High Yield Constrained Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] ICE BofA U.S. High Yield Constrained Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   8.50% 4.50%     6.44%                           6.65%            
LONG DURATION FUND | SIIT LONG DURATION FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   6.79% (4.22%)     2.84%                               4.18%        
Performance Inception Date Apr. 21, 2004                                                  
LONG DURATION FUND | SIIT LONG DURATION FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   4.62% (5.97%)     0.50%                               1.73%        
LONG DURATION FUND | SIIT LONG DURATION FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   3.99% (3.80%)     1.33%                               2.30%        
LONG DURATION FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%                               3.29%        
LONG DURATION FUND | The Fund’s 70/30 Blended Benchmark Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] The Fund’s 70/30 Blended Benchmark Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.13% (4.18%)     2.43%                               4.68%        
LONG DURATION CREDIT FUND | SIIT Long Duration Credit Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   7.36% (3.67%)     2.92%           3.21%                            
Performance Inception Date Jun. 29, 2012                                                  
LONG DURATION CREDIT FUND | SIIT Long Duration Credit Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   5.18% (5.49%)     0.96%           1.19%                            
LONG DURATION CREDIT FUND | SIIT Long Duration Credit Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   4.32% (3.41%)     1.50%           1.65%                            
LONG DURATION CREDIT FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%           1.94%                            
LONG DURATION CREDIT FUND | Bloomberg Long A+ U.S. Credit Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg Long A+ U.S. Credit Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.54% (3.69%)     2.59%           2.78%                            
ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   5.07% 3.23%     2.72%                 2.19%                      
Performance Inception Date Feb. 28, 2011                                                  
ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   3.14% 1.87%     1.61%                 1.29%                      
ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   2.98% 1.88%     1.60%                 1.29%                      
ULTRA SHORT DURATION BOND FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%                 2.42%                      
ULTRA SHORT DURATION BOND FUND | Bloomberg Short U.S. Treasury 9‑12 Month Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg Short U.S. Treasury 9‑12 Month Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   4.40% 2.78%     2.18%                 1.55%                      
EMERGING MARKETS DEBT FUND | SIIT EMERGING MARKETS DEBT FUND - CLASS A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   20.34% 2.96%     5.06%                           5.27%            
Performance Inception Date Dec. 05, 2005                                                  
EMERGING MARKETS DEBT FUND | SIIT EMERGING MARKETS DEBT FUND - CLASS A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   16.83% 0.72%     3.20%                           3.13%            
EMERGING MARKETS DEBT FUND | SIIT EMERGING MARKETS DEBT FUND - CLASS A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   11.96% 1.22%     3.08%                           3.22%            
EMERGING MARKETS DEBT FUND | Bloomberg Global Aggregate Index (USD) Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg Global Aggregate Index (USD) Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   8.17% (2.15%)     1.26%                           2.55%            
EMERGING MARKETS DEBT FUND | The Fund’s Blended Benchmark Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] The Fund’s Blended Benchmark Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   16.79% 1.48%     4.19%                           4.96%            
REAL RETURN FUND | SIIT Real Return Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   6.53% 3.28%     3.10%                         3.04%              
Performance Inception Date Dec. 14, 2006                                                  
REAL RETURN FUND | SIIT Real Return Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   4.56% 1.33%     1.74%                         1.75%              
REAL RETURN FUND | SIIT Real Return Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   3.85% 1.65%     1.79%                         1.83%              
REAL RETURN FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%                         3.17%              
REAL RETURN FUND | Bloomberg 1‑5 Year U.S. TIPS Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg 1‑5 Year U.S. TIPS Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   6.55% 3.32%     3.16%                         3.01%              
LIMITED DURATION BOND FUND | SIIT Limited Duration Bond Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   5.87% 2.43%     2.49%     2.25%                                  
Performance Inception Date Jul. 31, 2014                                                  
LIMITED DURATION BOND FUND | SIIT Limited Duration Bond Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   4.01% 1.12%     1.38%     1.22%                                  
LIMITED DURATION BOND FUND | SIIT Limited Duration Bond Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   3.45% 1.29%     1.42%     1.27%                                  
LIMITED DURATION BOND FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%     2.00%                                  
LIMITED DURATION BOND FUND | ICE BofA 1‑3 Year US Treasury Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] ICE BofA 1‑3 Year US Treasury Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   5.09% 1.79%     1.85%     1.69%                                  
INTERMEDIATE DURATION CREDIT FUND | SIIT Intermediate Duration Credit Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   7.39% (0.19%)     3.01% 2.60%                                      
Performance Inception Date Mar. 31, 2015                                                  
INTERMEDIATE DURATION CREDIT FUND | SIIT Intermediate Duration Credit Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   5.38% (1.79%)     1.48% 1.10%                                      
INTERMEDIATE DURATION CREDIT FUND | SIIT Intermediate Duration Credit Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   4.34% (0.82%)     1.66% 1.35%                                      
INTERMEDIATE DURATION CREDIT FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01% 1.77%                                      
INTERMEDIATE DURATION CREDIT FUND | Bloomberg A+ U.S. Credit Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg A+ U.S. Credit Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.57% (0.35%)     2.60% 2.28%                                      
DYNAMIC ASSET ALLOCATION FUND | SIIT Dynamic Asset Allocation Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   20.26% 15.22%     14.53%                   14.31%                    
Performance Inception Date Jul. 30, 2010                                                  
DYNAMIC ASSET ALLOCATION FUND | SIIT Dynamic Asset Allocation Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   16.26% 10.40%     11.24%                   11.58%                    
DYNAMIC ASSET ALLOCATION FUND | SIIT Dynamic Asset Allocation Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   14.01% 10.84%     11.08%                   11.28%                    
DYNAMIC ASSET ALLOCATION FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] S&P 500 Index Return (reflects no deduction for fees, expenses or taxes)                                                  
Average Annual Return, Percent   17.88% 14.42%     14.82%                   14.69%                    
MULTI-ASSET REAL RETURN FUND | SIIT Multi-Asset Real Return Fund - Class A                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return Before Taxes                                                  
Average Annual Return, Percent   8.49% 6.48%     3.77%               1.37%                        
Performance Inception Date Jul. 28, 2011                                                  
MULTI-ASSET REAL RETURN FUND | SIIT Multi-Asset Real Return Fund - Class A | After Taxes on Distributions                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions                                                  
Average Annual Return, Percent   7.33% 3.69%     1.97%               0.05%                        
MULTI-ASSET REAL RETURN FUND | SIIT Multi-Asset Real Return Fund - Class A | After Taxes on Distributions and Sales                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Return After Taxes on Distributions and Sale of Fund Shares                                                  
Average Annual Return, Percent   5.13% 3.81%     2.14%               0.47%                        
MULTI-ASSET REAL RETURN FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   7.30% (0.36%)     2.01%               2.25%                        
MULTI-ASSET REAL RETURN FUND | The Fund’s Blended Benchmark Return (reflects no deductions for fees, expenses or taxes)                                                    
Prospectus [Line Items]                                                    
Average Annual Return, Label [Optional Text] The Fund’s Blended Benchmark Return (reflects no deductions for fees, expenses or taxes)                                                  
Average Annual Return, Percent   9.57% 6.04%     4.99%               2.58%