v3.25.1
Shareholder Report
 6 Months Ended
Mar. 31, 2025
USD ($)
shares
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Nicholas II, Inc.
Entity Central Index Key 0000723455
Entity Investment Company Type N-1A
Document Period End Date Mar. 31, 2025
CLASS I  
Shareholder Report [Line Items]  
Fund Name Nicholas II, Inc.
Class Name Class I
Trading Symbol NCTWX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Nicholas II, Inc. (the "Fund") - Class I (the "Class") for the period of October 1, 2024 to March 31, 2025.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.nicholasfunds.com. You can also request this information by contacting us at 1-800-544-6547.
Additional Information Phone Number 1-800-544-6547
Additional Information Website www.nicholasfunds.com
Expenses [Text Block]
What Were the Portfolio Costs for the Last Six Months?
(based on a hypothetical $10,000 investment)
Portfolio Name Costs of a $10,000 investment Annualized costs paid as a percentage of a $10,000 investment
Class I $29 0.59%
Expenses Paid, Amount $ 29
Expense Ratio, Percent 0.59%
Net Assets $ 1,018,447,632
Holdings Count | shares 69
Investment Company, Portfolio Turnover 17.28%
Additional Fund Statistics [Text Block]
Key Fund Statistics
As of March 31, 2025
Net Assets $1,018,447,632
Number of Portfolio Holdings 69
Portfolio Turnover Rate 17.28%
Holdings [Text Block]
Top Ten Equity Holdings
As of March 31, 2025
Name Percentage of Net Assets
CyberArk Software Ltd. 2.80%
O'Reilly Automotive, Inc. 2.42%
BJ's Wholesale Club Holdings, Inc. 2.41%
Corpay, Inc. 2.40%
Verisk Analytics Inc. 2.30%
Teledyne Technologies Incorporated 2.20%
TransUnion 2.05%
CBRE Group, Inc. Class A 2.03%
Dynatrace, Inc. 2.03%
Vulcan Materials Company 1.92%
Total of top ten 22.56%
Sector Diversification (As a Percentage of Total Investments)
As of March 31, 2025
Af Image
Largest Holdings [Text Block]
Top Ten Equity Holdings
As of March 31, 2025
Name Percentage of Net Assets
CyberArk Software Ltd. 2.80%
O'Reilly Automotive, Inc. 2.42%
BJ's Wholesale Club Holdings, Inc. 2.41%
Corpay, Inc. 2.40%
Verisk Analytics Inc. 2.30%
Teledyne Technologies Incorporated 2.20%
TransUnion 2.05%
CBRE Group, Inc. Class A 2.03%
Dynatrace, Inc. 2.03%
Vulcan Materials Company 1.92%
Total of top ten 22.56%
CLASS N  
Shareholder Report [Line Items]  
Fund Name Nicholas II, Inc.
Class Name Class N
Trading Symbol NNTWX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Nicholas II, Inc. (the "Fund") - Class N (the "Class") for the period of October 1, 2024 to March 31, 2025.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Fund at www.nicholasfunds.com. You can also request this information by contacting us at 1-800-544-6547.
Additional Information Phone Number 1-800-544-6547
Additional Information Website www.nicholasfunds.com
Expenses [Text Block]
What Were the Portfolio Costs for the Last Six Months?
(based on a hypothetical $10,000 investment)
Portfolio Name Costs of a $10,000 investment Annualized costs paid as a percentage of a $10,000 investment
Class N $44 0.90%
Expenses Paid, Amount $ 44
Expense Ratio, Percent 0.90%
Net Assets $ 1,018,447,632
Holdings Count | shares 69
Investment Company, Portfolio Turnover 17.28%
Additional Fund Statistics [Text Block]
Key Fund Statistics
As of March 31, 2025
Net Assets $1,018,447,632
Number of Portfolio Holdings 69
Portfolio Turnover Rate 17.28%
Holdings [Text Block]
Top Ten Equity Holdings
As of March 31, 2025
Name Percentage of Net Assets
CyberArk Software Ltd. 2.80%
O'Reilly Automotive, Inc. 2.42%
BJ's Wholesale Club Holdings, Inc. 2.41%
Corpay, Inc. 2.40%
Verisk Analytics Inc. 2.30%
Teledyne Technologies Incorporated 2.20%
TransUnion 2.05%
CBRE Group, Inc. Class A 2.03%
Dynatrace, Inc. 2.03%
Vulcan Materials Company 1.92%
Total of top ten 22.56%
Sector Diversification (As a Percentage of Total Investments)
As of March 31, 2025
Af Image
Largest Holdings [Text Block]
Top Ten Equity Holdings
As of March 31, 2025
Name Percentage of Net Assets
CyberArk Software Ltd. 2.80%
O'Reilly Automotive, Inc. 2.42%
BJ's Wholesale Club Holdings, Inc. 2.41%
Corpay, Inc. 2.40%
Verisk Analytics Inc. 2.30%
Teledyne Technologies Incorporated 2.20%
TransUnion 2.05%
CBRE Group, Inc. Class A 2.03%
Dynatrace, Inc. 2.03%
Vulcan Materials Company 1.92%
Total of top ten 22.56%