v3.26.1
Loans and Allowance for Credit Losses - Summary of Inclusive Capitalized Loans (Detail) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Dec. 31, 2024
Student Loan Portfolio By Program [Line Items]        
Total loans $ 2,607,209 $ 2,551,705    
Loans held for sale, at lower of amortized cost or fair value 10,786 15,144    
Total loans, gross 2,490,513 2,436,916    
Bank Holding Company Accounting [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 2,617,995 2,566,849 $ 2,486,433 $ 2,491,022
Total loans, gross $ 2,617,995 $ 2,566,849    
Percentage of total gross loans [1] 100.00% 100.00%    
Bank Holding Company Accounting [Member] | Loans Held for Investment [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 2,607,209 $ 2,551,705    
Percentage of total gross loans [1] 100.00% 99.00%    
Bank Holding Company Accounting [Member] | Loans Held for Sale at Lower of Amortized Cost or Fair Value [Member]        
Student Loan Portfolio By Program [Line Items]        
Loans held for sale, at lower of amortized cost or fair value $ 10,786 $ 15,144    
Percentage of total gross loans [1] 0.00% 0.00%    
Recreation [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 1,671,538 $ 1,617,221    
Recreation [Member] | Bank Holding Company Accounting [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 1,671,538 1,617,221 1,545,844 1,543,243
Recreation [Member] | Bank Holding Company Accounting [Member] | Loans Held for Investment [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 1,671,538 $ 1,617,221    
Percentage of total gross loans [1] 64.00% 63.00%    
Home Improvement [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 814,933 $ 810,237    
Home Improvement [Member] | Bank Holding Company Accounting [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 814,933 810,237 812,381 827,211
Home Improvement [Member] | Bank Holding Company Accounting [Member] | Loans Held for Investment [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 814,933 $ 810,237    
Percentage of total gross loans [1] 31.00% 32.00%    
Commercial [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 119,612 $ 123,068    
Commercial [Member] | Bank Holding Company Accounting [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 119,612 123,068 116,059 111,273
Commercial [Member] | Bank Holding Company Accounting [Member] | Loans Held for Investment [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 119,612 $ 123,068    
Percentage of total gross loans [1] 5.00% 5.00%    
Taxi Medallion [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans $ 1,126 $ 1,179    
Taxi Medallion [Member] | Bank Holding Company Accounting [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 1,126 1,179 1,650 1,909
Taxi Medallion [Member] | Bank Holding Company Accounting [Member] | Loans Held for Investment [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 1,126 1,179    
Strategic Partnership [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 10,786 15,144    
Strategic Partnership [Member] | Bank Holding Company Accounting [Member]        
Student Loan Portfolio By Program [Line Items]        
Total loans 10,786 15,144 $ 10,499 $ 7,386
Strategic Partnership [Member] | Bank Holding Company Accounting [Member] | Loans Held for Sale at Lower of Amortized Cost or Fair Value [Member]        
Student Loan Portfolio By Program [Line Items]        
Loans held for sale, at lower of amortized cost or fair value $ 10,786 $ 15,144    
[1]

(1) Percentage may not foot due to rounding.