Senior Securities - Summary of Senior Securities (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Facility
Line Of Credit Facility [Line Items]
Total Amount Outstanding	$ 202,033	$ 123,890	$ 154,480	$ 120,454	$ 108,498	$ 82,000	$ 57,000	$ 100,500	$ 124,500	$ 70,000	$ 45,000
Asset Coverage Per Unit	5,371	6,906	11,020	9,508	5,812	5,221	6,513	4,056	3,076	5,356	8,176
Involuntary Liquidating Preference Per Unit	0	0	0	0	0	0	0	0	0	0	0
Preferred Interests
Line Of Credit Facility [Line Items]
Total Amount Outstanding										134,000	134,000
Asset Coverage Per Unit										51,592	68,125
Involuntary Liquidating Preference Per Unit										20,074	20,075
Funding Facility I
Line Of Credit Facility [Line Items]
Total Amount Outstanding					158,000	212,000	175,000	175,000	229,000	125,000	50,000
Asset Coverage Per Unit					5,812	5,221	6,513	4,056	3,076	5,356	8,176
Involuntary Liquidating Preference Per Unit		0	0	0	0	0	0	0	0	0	$ 0
Funding Facility II
Line Of Credit Facility [Line Items]
Total Amount Outstanding	100,000	100,000		36,000
Asset Coverage Per Unit	5,371	6,906		9,508
Involuntary Liquidating Preference Per Unit	0	0	0	0
SBA Debentures
Line Of Credit Facility [Line Items]
Total Amount Outstanding	150,000	150,000	150,000	138,000	138,000	98,000	83,000	61,000	42,800	28,000
Asset Coverage Per Unit	5,371	6,906	11,020	9,508	5,812	5,221	6,513	4,056	3,076	5,356
Involuntary Liquidating Preference Per Unit	0	0	0	0	0	0	0	0	0	0
2019 Convertible Notes
Line Of Credit Facility [Line Items]
Total Amount Outstanding						108,000	108,000	108,000	108,000	108,000
Asset Coverage Per Unit						2,157	2,335	2,352	2,429	3,617
Involuntary Liquidating Preference Per Unit	0	0	0	0	0	0	0	0	$ 0	$ 0
2022 Convertible Notes
Line Of Credit Facility [Line Items]
Total Amount Outstanding			140,000	140,000	140,000	140,000	140,000	140,000
Asset Coverage Per Unit			1,948	2,058	1,992	2,157	2,335	2,352
Involuntary Liquidating Preference Per Unit	0	0	0	0	0	0	0	$ 0
2022 Notes
Line Of Credit Facility [Line Items]
Total Amount Outstanding				175,000	175,000	175,000	175,000
Asset Coverage Per Unit				2,058	1,992	2,157	2,335
Involuntary Liquidating Preference Per Unit	0	0	0	0	0	$ 0	$ 0
2024 Notes
Line Of Credit Facility [Line Items]
Total Amount Outstanding	250,000	250,000	250,000	250,000	200,000
Asset Coverage Per Unit	1,855	1,929	1,948	2,058	1,992
Involuntary Liquidating Preference Per Unit	0	0	0	$ 0	$ 0
2026 Notes
Line Of Credit Facility [Line Items]
Total Amount Outstanding	325,000	325,000	325,000
Asset Coverage Per Unit	1,855	1,929	1,948
Involuntary Liquidating Preference Per Unit	$ 0	$ 0	$ 0