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Investment Company, Expense Ratio Before Fee Waiver And Reimbursements

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Investment Company, Expense Ratio Including Fee Waiver And Reimbursements

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Investment Company, Ratio To Average Net Assets

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Per share or unit amount of distribution to shareholders. Includes, but is not limited to, dividend and capital gain. Excludes distribution for tax return of capital.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Per share or unit amount of realized and unrealized gain (loss) on investment.

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Per share or unit amount of investment income (loss) and realized and unrealized gain (loss) on investment.

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Per share or unit amount, after investment expense, of dividend and interest investment income (loss).

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Percentage of investment income (loss) to average net assets.

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Percentage increase (decrease) in fund net asset value, assuming reinvestment of dividends and capital gain distributions.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Average amount outstanding of long-term debt.

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Net asset value per share or per unit of investments in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes fair value disclosure.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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Financial Highlights - Summary (Details) $ / shares in Units, € in Thousands, £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2022 GBP (£) shares	Dec. 31, 2022 EUR (€) shares	Dec. 31, 2021 GBP (£) shares
Investment Company, Financial Highlights [Roll Forward]
Net asset value, beginning balance (in dollars per share) \| $ / shares	$ 13.49	$ 12.62	$ 13.26	$ 13.22	$ 13.63
Net investment income (in dollars per share) \| $ / shares	1.18	1.21	1.20	1.37	1.39
Net realized and unrealized (losses) gains (in dollars per share) \| $ / shares	(0.43)	0.86	(0.60)	0.03	(0.44)
Total net increase (in dollars per share) \| $ / shares	0.75	2.07	0.60	1.40	0.95
Distributions declared to stockholders from net investment income (in dollars per share) \| $ / shares	(1.22)	(1.20)	(1.24)	(1.36)	(1.36)
Net asset value, ending balance (in dollars per share) \| $ / shares	13.02	13.49	12.62	13.26	13.22
Per share market value (in dollars per share) \| $ / shares	$ 12.37	$ 13.70	$ 11.36	$ 13.74	$ 12.58
Total return based on market value	(0.56%)	31.91%	(5.24%)	20.45%	2.70%
Total return based on net asset value	5.71%	16.97%	5.52%	10.90%	7.16%
Shares outstanding at end of period (in shares) \| shares	100,937,026	97,907,441	96,827,342	96,827,342	76,106,372	100,937,026	100,937,026	97,907,441
Average weighted shares outstanding for the period (in shares) \| shares	100,202,847	96,952,959	96,827,342	85,209,378	76,022,375
Average net assets for the period	$ 1,344,266	$ 1,261,338	$ 1,168,043	$ 1,154,615	$ 1,026,313
Ratio to average net assets:
Net investment income	8.82%	9.32%	10.05%	10.15%	10.33%
Total expenses, before waivers/reimbursements	13.35%	13.11%	14.56%	14.87%	12.90%
Total expenses, net of waivers/reimbursements	13.01%	12.05%	13.39%	13.80%	12.22%
Asset coverage ratio	177.42%	181.21%	180.68%	173.98%	181.37%	177.42%	177.42%	181.21%
Portfolio turnover	18.01%	35.33%	15.43%	11.58%	36.75%
Common stock issuances (in dollars per share) \| $ / shares	$ 0.01	$ (0.01)	$ 0.00	$ 0.08	$ 0.00
Convertible Notes
Ratio to average net assets:
Average debt outstanding	$ 228,806	$ 201,250	$ 201,250	$ 234,332	$ 197,058
SBA-guaranteed debentures
Ratio to average net assets:
Average debt outstanding	300,000	300,000	285,852	179,408	158,471
Unsecured Notes
Ratio to average net assets:
Average debt outstanding	526,829	516,611	453,250	414,949	266,296
Holdings Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Credit facility outstanding balance	618,963	545,263	450,163
Holdings Credit Facility \| Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Average debt outstanding	581,367	478,016	526,645	598,129	384,433
NMFC Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Credit facility outstanding balance	40,359	127,192	165,500			£ 22,900	€ 700	£ 16,400
NMFC Credit Facility \| Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Average debt outstanding	133,053	132,685	155,497	105,533	117,719
DB Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Credit facility outstanding balance	186,400	226,300	244,000
DB Credit Facility \| Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Average debt outstanding	209,898	209,307	233,649	113,967	49,833
NMNLC Credit Facility \| Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Average debt outstanding	0	0	0	1,471	3,570
NMNLC Credit Facility II \| Revolving Credit Facility
Ratio to average net assets:
Credit facility outstanding balance	3,785	15,200
NMNLC Credit Facility II \| Credit Facility \| Revolving Credit Facility
Ratio to average net assets:
Average debt outstanding	$ 7,195	$ 3,501	$ 0	$ 0	$ 0