Net Assets (Tables)
 9 Months Ended
Sep. 30, 2023
Equity [Abstract]  
Schedule of Net Assets
The table below illustrates the effect of certain transactions on the net asset accounts of the Company during the three and nine months ended September 30, 2023:
Accumulated Overdistributed Earnings
 Common StockPaid in
Capital in
Excess		Accumulated
Net Investment		Accumulated Net Realized Net 
Unrealized Appreciation		Total Net AssetsNon-
Controlling
Interest in		Total
 SharesPar Amountof ParIncome(Losses) Gains(Depreciation)of NMFCNMNLCNet Assets
Net assets at December 31, 2022100,937,026 $1,009 $1,305,945 $147,593 $(68,072)$(72,002)$1,314,473 $11,718 $1,326,191 
Issuances of common stock— — — — — — — — — 
Offering costs— — (56)— — — (56)— (56)
Distributions declared — — — (32,300)— — (32,300)(153)(32,453)
Net increase in net assets resulting from operations— — — 38,113 677 5,783 44,573 239 44,812 
Net assets at March 31, 2023100,937,026 $1,009 $1,305,889 $153,406 $(67,395)$(66,219)$1,326,690 $11,804 $1,338,494 
Issuances of common stock— — — — — — — — — 
Offering costs— — (91)— — — (91)— (91)
Distributions declared— — — (35,328)— — (35,328)(191)(35,519)
Net increase (decrease) in net assets resulting from operations— — — 39,678 2,567 (7,415)34,830 248 35,078 
Net assets at June 30, 2023100,937,026 $1,009 $1,305,798 $157,756 $(64,828)$(73,634)$1,326,101 $11,861 $1,337,962 
Issuances of common stock502,623 5 6,620 — — — 6,625 — 6,625 
Offering costs— — (66)— — — (66)— (66)
Distributions declared — — — (36,338)— — (36,338)(188)(36,526)
Net increase (decrease) in net assets resulting from operations— — — 40,445 4,673 (16,422)28,696 3 28,699 
Net assets at September 30, 2023101,439,649 $1,014 $1,312,352 $161,863 $(60,155)$(90,056)$1,325,018 $11,676 $1,336,694 
    
The table below illustrates the effect of certain transactions on the net asset accounts of the Company during the three and nine months ended September 30, 2022:
Accumulated Undistributed (Overdistributed) Earnings
 Common StockPaid in
Capital in Excess		Accumulated
Net Investment		Accumulated Net Realized 
(Losses)		Net 
Unrealized Appreciation		Total Net AssetsNon-Controlling Interest inTotal
 SharesPar Amountof ParIncomeGains(Depreciation)of NMFCNMNLCNet Assets
Net assets at December 31, 202197,907,441 $979 $1,272,796 $118,330 $(92,099)$21,239 $1,321,245 $21,367 $1,342,612 
Issuances of common stock1,591,121 16 21,556 — — — 21,572 — 21,572 
Offering costs— — (52)— — — (52)— (52)
Distributions declared— — — (29,589)— — (29,589)(3,750)(33,339)
Net increase (decrease) in net assets resulting from operations— — — 29,573 17,596 (10,977)36,192 855 37,047 
Net assets at March 31, 202299,498,562 $995 $1,294,300 $118,314 $(74,503)$10,262 $1,349,368 $18,472 $1,367,840 
Issuances of common stock1,218,366 1216,565 — — — 16,577 — 16,577 
Offering costs— — (74)— — — (74)— (74)
Distributions declared— — — (30,215)— — (30,215)(4,190)(34,405)
Contributions related to non-controlling interest in NMNLC— — — — — — — 123 123 
Net increase (decrease) in net assets resulting from operations— — — 31,396 14,849 (30,291)15,954 (814)15,140 
Net assets at June 30, 2022100,716,928 $1,007 $1,310,791 $119,495 $(59,654)$(20,029)$1,351,610 $13,591 $1,365,201 
Issuances of common stock220,098 2 2,953 — — — 2,955 — 2,955 
Offering costs— — (34)— — — (34)— (34)
Distributions declared— — — (30,281)— — (30,281)(257)(30,538)
Net increase (decrease) in net assets resulting from operations— — — 32,527 (390)(24,432)7,705 (191)7,514 
Net assets at September 30, 2022100,937,026 $1,009 $1,313,710 $121,741 $(60,044)$(44,461)$1,331,955 $13,143 $1,345,098