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Summary of Significant Accounting Policies - Narrative (Details)
 11 Months Ended 12 Months Ended
Jul. 01, 2024
USD ($)
$ / shares
shares
Mar. 30, 2020
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
Dec. 31, 2024
USD ($)
numberOfAgreement
Dec. 31, 2023
USD ($)
numberOfAgreement
Dec. 31, 2022
USD ($)
Feb. 04, 2016
USD ($)
Securities Financing Transaction [Line Items]              
Number of collateralized agreements | numberOfAgreement       1 1    
Cost basis of securities purchased under collateralized agreements to resell       $ 30,000,000 $ 30,000,000    
Fair value of securities purchased under collateralized agreements to resell       13,500,000 16,500,000    
Cash equivalents       0 0    
Investment income, interest, paid-in-kind       36,870,000 33,594,000 $ 17,326,000  
Investment income, dividend, paid-in-kind       $ 31,575,000 27,409,000 22,543,000  
Investments threshold period past due for nonaccrual status       30 days      
Income tax expense (benefit)       $ 2,376,000 1,762,000 9,299,000  
Current income tax expense       262,000 418,000 825,000  
Deferred income tax provision       2,114,000 1,344,000 $ 8,474,000  
Deferred tax liability       $ 1,410,000 0    
Dividend reinvestment plan, share price percentage, threshold       110.00%      
Investments in Majority-owned Subsidiaries              
Securities Financing Transaction [Line Items]              
Shares redeemed for a promissory note (in shares) | shares   105,030          
Redemption of shares paid-in-kind   $ 11,315,000          
Interest rate   7.00%          
Common Stock              
Securities Financing Transaction [Line Items]              
Stock repurchase program, authorized amount             $ 50,000,000
Common stock repurchased     $ 2,948,000 $ 0 $ 0    
Common Stock | New Mountain Net Lease Corporation              
Securities Financing Transaction [Line Items]              
Sale of stock, number of shares issued (in shares) | shares   105,030          
Sale of stock, price per share (in dollars per share) | $ / shares   $ 107.73          
Sale of stock, consideration received   $ 11,315,000          
Common Stock | New Mountain Net Lease Corporation | Investments in Majority-owned Subsidiaries              
Securities Financing Transaction [Line Items]              
Sale of stock, price per share (in dollars per share) | $ / shares $ 73.39            
Sale of stock, consideration received $ 4,666,000            
Common Stock | Affiliate Of Investment Adviser | New Mountain Net Lease Corporation              
Securities Financing Transaction [Line Items]              
Sale of stock, number of shares issued (in shares) | shares 63,575            
Sale of stock, price per share (in dollars per share) | $ / shares $ 73.39            
Sale of stock, consideration received $ 4,666,000