Consolidated Statements of Operations - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
Investment income        
PIK interest income $ 7,917 $ 6,193 $ 24,807 $ 21,993
Non-cash dividend income 6,988 5,995 20,225 16,338
Total investment income 94,349 78,449 281,794 220,522
Expenses        
Interest and other financing expenses 31,425 24,648 93,921 63,957
Management fee 11,334 11,717 34,549 35,040
Incentive fee 10,169 8,202 29,748 23,605
Administrative expenses 995 881 2,996 3,022
Professional fees 850 775 2,818 2,529
Other general and administrative expenses 542 545 1,543 1,540
Total expenses 55,315 46,768 165,575 129,693
Less: management fee waived (See Note 5) (1,013) (1,115) (3,172) (3,349)
Less: expenses waived and reimbursed (See Note 5) 0 0 0 (238)
Net expenses 54,302 45,653 162,403 126,106
Net investment income before income taxes 40,047 32,796 119,391 94,416
Income tax (benefit) expense (627) (13) 401 (5)
Net investment income 40,674 32,809 118,990 94,421
Net realized gains (losses):        
Investments     7,904 35,468
Foreign currency 0 (166) 13 219
Net change in unrealized (depreciation) appreciation:        
Investments     (18,340) (67,634)
Securities purchased under collateralized agreements to resell 0 0 (39) (2,021)
Foreign currency (60) (10) (5) (625)
Benefit (provision) for taxes 291 30 66 (127)
Net realized and unrealized losses (11,975) (25,295) (10,401) (34,720)
Net increase in net assets resulting from operations 28,699 7,514 108,589 59,701
Less: Net (increase) decrease in net assets resulting from operations related to non-controlling interest in New Mountain Net Lease Corporation (3) 191 (490) 150
Net increase in net assets resulting from operations related to New Mountain Finance Corporation $ 28,696 $ 7,705 $ 108,099 $ 59,851
Basic earnings per share (in dollars per share) $ 0.28 $ 0.08 $ 1.07 $ 0.60
Weighted average shares of common stock outstanding - basic (in shares) 100,954,898 100,830,075 100,943,049 99,955,432
Diluted earnings per share (in dollars per share) $ 0.27 $ 0.08 $ 0.98 $ 0.59
Weighted average shares of common stock outstanding - diluted (in shares) 123,183,269 114,087,660 124,595,709 113,213,017
Distributions declared per share (in dollars per share) $ 0.36 $ 0.30 $ 1.03 $ 0.90
Distributions paid per share (in dollars per share) $ 0.36 $ 0.30 $ 1.03 $ 0.90
Non-controlled/Non-affiliated        
Investment income        
Interest income (excluding Payment-in-kind ("PIK") interest income) $ 63,892 $ 49,401 $ 189,299 $ 127,934
PIK interest income 4,061 2,688 11,772 8,924
Dividend income 49 9 143 144
Non-cash dividend income 4,458 3,837 12,929 10,111
Other income 791 1,517 3,395 7,435
Net realized gains (losses):        
Investments 113 (239) (8,509) (903)
Net change in unrealized (depreciation) appreciation:        
Investments 12,419 (31,944) 11,664 (56,975)
Non-controlled/Affiliated        
Investment income        
Interest income (excluding Payment-in-kind ("PIK") interest income) 884 270 1,576 788
PIK interest income 265 264 1,370 773
Non-cash dividend income 1,173 1,042 3,417 3,036
Other income 63 62 189 187
Net change in unrealized (depreciation) appreciation:        
Investments (14,815) (13,381) (14,830) 377
Controlled        
Investment income        
Interest income (excluding Payment-in-kind ("PIK") interest income) 1,351 2,914 4,038 6,285
PIK interest income 3,591 3,241 11,665 12,296
Dividend income 11,041 9,867 34,179 32,183
Non-cash dividend income 1,357 1,116 3,879 3,191
Other income 1,373 2,221 3,943 7,235
Net realized gains (losses):        
Investments 4,560 17 16,413 36,371
Net change in unrealized (depreciation) appreciation:        
Investments $ (14,483) $ 20,398 $ (15,174) $ (11,036)