Consolidated Statements of Changes in Net Assets - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance		$ 652,285	$ 560,000	$ 406,917
Balance, shares		30,887,360	20,862,314	13,358,289	8,597,116
Par Amount		$ 21.12	$ 19.88	$ 19.50	$ 19.43
Net increase (decrease) in net assets resulting from operations:
Net investment income		$ 59,729	$ 47,626	$ 49,880
Net realized gain (loss) on investments, foreign currency transactions and foreign currency forwards		4,945	32,615	(15,286)
Realized loss on asset acquisition	[1]			3,825
Acquisition of Alcentra Capital Corporation, net of cash acquired	[1]			(12,884)
Net change in unrealized appreciation (depreciation) on investments, foreign currency forward contracts and foreign currency translation		(48,324)	4,789	24,092
Benefit (provision) for taxes on realized gain on investments		(911)	(1,177)	46
Benefit (provision) for taxes on unrealized appreciation (depreciation) on investments		$ 105	$ (220)	$ (235)
Issuance of common stock, par amount		$ 1.79	$ 1.69	$ 1.64	1.64
Issuance of common stock			$ 52,632	$ 44,297
Issuance in connection with asset acquisition (Note 14), value				101,949
Deemed contribution from the Advisor (Note 3)			5,386
Equity offering costs			(523)
Issuance of common shares pursuant to dividend reinvestment plan, value				589
Repurchase of common stock, value				2,208
Distributions from distributable earnings		$ (55,288)	$ (48,843)	$ (46,216)
Total increase (decrease), par amount		$ (1.29)	$ 1.24	$ 0.38	$ 0.07
Total increase (decrease)		$ 612,541	$ 92,285	$ 153,083
Balance		$ 612,541	$ 652,285	$ 560,000	$ 406,917
Balance, shares		30,887,360	30,887,360	20,862,314	13,358,289
Par Amount		$ 19.83	$ 21.12	$ 19.88	$ 19.50
Common Stock
Balance, shares		30,887,360	28,167,360	20,862,314
Par Amount		$ 31	$ 28	$ 21
Net increase (decrease) in net assets resulting from operations:
Issuance of common stock, share			2,720,000	2,265,021
Issuance of common stock, par amount			$ 3	$ 2
Issuance in connection with asset acquisition (Note 14), share				5,202,312
Issuance in connection with asset acquisition (Note 14), par amount				$ 5
Issuance of common shares pursuant to dividend reinvestment plan, share				30,128
Repurchase of common stock, share				(192,415)
Total increase (decrease), share		30,887,360	2,720,000	7,305,046
Total increase (decrease), par amount		$ 31	$ 3	$ 7
Balance, shares		30,887,360	30,887,360	28,167,360	20,862,314
Par Amount		$ 31	$ 31	$ 28	$ 21
Paid in Capital in Excess of Par Value
Balance		$ 666,162	$ 594,658	$ 414,293
Net increase (decrease) in net assets resulting from operations:
Issuance of common stock			52,629	44,295
Issuance in connection with asset acquisition (Note 14), value				101,944
Deemed contribution from the Advisor (Note 3)			5,386
Equity offering costs			(523)
Issuance of common shares pursuant to dividend reinvestment plan, value				589
Repurchase of common stock, value				(2,208)
Total increase (decrease)		666,162	57,492	144,620
Tax reclassification of stockholders' equity in accordance with GAAP (Note 11)		8,846	14,012	35,745
Balance		675,008	666,162	594,658	$ 414,293
Accumulated Earnings (Loss)
Balance		(13,908)	(34,686)	(7,397)
Net increase (decrease) in net assets resulting from operations:
Net investment income		59,729	47,626	49,880
Net realized gain (loss) on investments, foreign currency transactions and foreign currency forwards		4,945	32,615	(15,286)
Realized loss on asset acquisition				3,825
Net change in unrealized appreciation (depreciation) on investments, foreign currency forward contracts and foreign currency translation		(48,324)	4,789	24,092
Benefit (provision) for taxes on realized gain on investments		(911)	(1,177)	46
Benefit (provision) for taxes on unrealized appreciation (depreciation) on investments		105	(220)	(235)
Distributions from distributable earnings		(55,288)	(48,843)	(46,216)
Total increase (decrease)		(53,652)	34,790	8,456
Tax reclassification of stockholders' equity in accordance with GAAP (Note 11)		(8,846)	(14,012)	(35,745)
Balance		$ (62,498)	$ (13,908)	$ (34,686)	$ (7,397)

[1] After the close of business on January 31, 2020, in connection with the Alcentra Acquisition (as defined in Note 1 and further discussed in Note 14), the Company acquired net assets of $114,431 which included $195,682 of investments, $3,409 cash and cash equivalents and $1,398 of other assets, net of $86,058 of assumed liabilities, for the total cash and stock consideration of $118,256, inclusive of $7,250 of asset acquisition costs.