Fair Value Measures and Disclosures - Schedule of Fair Value Measurement Inputs and Valuation Techniques (Details)	Mar. 31, 2023 USD ($) $ / shares		Dec. 31, 2022 USD ($) $ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 1,723,352,000	[1]	$ 1,760,030,000
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	1,629,058,000		1,716,054,000
Level 3 | Senior secured first lien debt | Discounted Cash Flow | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 1,258,936,000		$ 1,471,816,000
Level 3 | Senior secured first lien debt | Discounted Cash Flow | Minimum | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.065		0.065
Level 3 | Senior secured first lien debt | Discounted Cash Flow | Maximum | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.350		0.340
Level 3 | Senior secured first lien debt | Discounted Cash Flow | Weighted Average | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.139		0.147
Level 3 | Senior secured first lien debt | Broker Quotes | Broker Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 124,286,000		$ 79,035,000
Level 3 | Senior secured first lien debt | Market Comparable Approach | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	45,643,000		20,050,000
Level 3 | Senior secured first lien debt | Market Comparable Approach | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	39,376,000		3,552,000
Level 3 | Senior secured first lien debt | Market Comparable Approach | $ per kW
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 3,837,000		$ 4,527,000
Measurement input	131.85		131.85
Level 3 | Senior secured first lien debt | Market Comparable Approach | Minimum | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.20		0.25
Level 3 | Senior secured first lien debt | Market Comparable Approach | Minimum | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	5.75		2.75
Level 3 | Senior secured first lien debt | Market Comparable Approach | Maximum | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1.55		1.70
Level 3 | Senior secured first lien debt | Market Comparable Approach | Maximum | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	12.5		4.25
Level 3 | Senior secured first lien debt | Market Comparable Approach | Weighted Average | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.62		1.19
Level 3 | Senior secured first lien debt | Market Comparable Approach | Weighted Average | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	10.45		4.09
Level 3 | Senior secured first lien debt | Other Valuation Technique
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 375,000		$ 532,000
Level 3 | Senior secured second lien debt | Discounted Cash Flow | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 38,997,000		$ 38,769,000
Level 3 | Senior secured second lien debt | Discounted Cash Flow | Minimum | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.103		0.143
Level 3 | Senior secured second lien debt | Discounted Cash Flow | Maximum | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.225		0.215
Level 3 | Senior secured second lien debt | Discounted Cash Flow | Weighted Average | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.156		0.172
Level 3 | Collateralized securities and structured products - equity | Discounted Cash Flow | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 1,133,000		$ 1,179,000
Measurement input	0.210		0.210
Level 3 | Unsecured debt | Discounted Cash Flow | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 7,385,000		$ 7,327,000
Measurement input			0.177
Level 3 | Unsecured debt | Discounted Cash Flow | Maximum | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.165
Level 3 | Unsecured debt | Market Comparable Approach | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value			$ 15,316,000
Measurement input			9.25
Level 3 | Unsecured debt | Contingent Claims Analysis | Expected Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 8,132,000
Measurement input	1.100
Level 3 | Equity | Discounted Cash Flow | Discount Rates
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value			$ 2,238,000
Measurement input			0.168
Level 3 | Equity | Broker Quotes | Broker Quotes
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 1,075,000		$ 1,234,000
Level 3 | Equity | Market Comparable Approach | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	7,940,000		13,038,000
Level 3 | Equity | Market Comparable Approach | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	69,263,000		33,441,000
Level 3 | Equity | Market Comparable Approach | $ per kW
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 22,680,000		$ 23,995,000
Measurement input | $ / shares	425		412.5
Level 3 | Equity | Market Comparable Approach | Minimum | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.13		0.13
Level 3 | Equity | Market Comparable Approach | Minimum | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	3.75		2.75
Level 3 | Equity | Market Comparable Approach | Maximum | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	6.00		5.75
Level 3 | Equity | Market Comparable Approach | Maximum | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	15.50		14.55
Level 3 | Equity | Market Comparable Approach | Weighted Average | Revenue Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	3.25		2.93
Level 3 | Equity | Market Comparable Approach | Weighted Average | EBITDA Multiple
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	10.08		7.02
Level 3 | Equity | Options Pricing Model | Expected Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 0		$ 5,000
Level 3 | Equity | Options Pricing Model | Minimum | Expected Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.600		0.800
Level 3 | Equity | Options Pricing Model | Maximum | Expected Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.950		0.900
Level 3 | Equity | Options Pricing Model | Weighted Average | Expected Volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input			0.873

[1] Fair value determined in good faith by the Company’s board of directors (see Note 9), including via delegation to CIM as the Company’s valuation designee (see Note 2), using significant unobservable inputs unless otherwise noted.