Investment Portfolio - Balance Sheet Information for SIIJV (Details) - USD ($) $ in Thousands	Jun. 30, 2023		Mar. 31, 2023	Dec. 31, 2022		Jun. 30, 2022	Dec. 31, 2021	Mar. 31, 2021
Schedule of Investments [Line Items]
Investments, at fair value	$ 1,495,602	[1],[2]		$ 2,047,115	[3],[4]
Total assets	1,758,300			2,558,781
Total liabilities	78,577			805,033
Total shareholders' equity	1,679,723		$ 1,712,828	1,753,748		$ 1,791,255	$ 1,602,323	$ 1,783,915
Sustainable Infrastructure Investments, LLC
Schedule of Investments [Line Items]
Investments, at fair value	267,244			275,058
Cash and other assets	16,037			10,380
Total assets	283,281			285,438
Debt	206,303			213,583
Other liabilities	4,105			3,358
Total liabilities	210,408			216,941
Total shareholders' equity	$ 72,873			$ 68,497

[1] Security may be an obligation of one or more entities affiliated with the named company.

[2] See Note 8 for additional information regarding the fair value of the Company’s financial instruments.

[3] Security may be an obligation of one or more entities affiliated with the named company.

[4] See Note 8 for additional information regarding the fair value of the Company’s financial instruments.