Debt and Foreign Currency Transactions and Translations - Summary Company's outstanding debt obligations (Details) - USD ($) $ in Thousands		Sep. 30, 2023		Dec. 31, 2022
Debt Instrument [Line Items]
Aggregate Principal Committed		$ 4,481,153		$ 3,835,000
Outstanding Principal		2,405,759		2,193,588
Carrying Value		2,392,137		2,193,128	[1]
Fair Value		2,388,849	[2]	2,185,031	[3]
Unused Portion		2,075,394	[4]	1,641,412	[5]
Amount Available		1,912,896	[6]	1,010,441	[7]
Deferred Financing Costs and Debt Discount		(21,481)		(20,508)	[1]
Total Debt Obligations, net of Deferred Financing Cost and Debt Discount		2,370,656		2,172,620	[1]
Cardinal Funding LLC
Debt Instrument [Line Items]
Aggregate Principal Committed		800,000		800,000
Outstanding Principal		601,770		498,731
Carrying Value		601,770		498,731	[1]
Fair Value		599,782	[2]	495,510	[3]
Unused Portion		198,230	[4]	301,269	[5]
Amount Available		64,736	[6]	163,459	[7]
Grouse Funding LLC
Debt Instrument [Line Items]
Aggregate Principal Committed		250,000		250,000
Outstanding Principal		187,500		158,000
Carrying Value		187,500		158,000	[1]
Fair Value		187,500	[2]	158,000	[3]
Unused Portion		62,500	[4]	92,000	[5]
Amount Available		33,496	[6]	42,157	[7]
Mallard Funding LLC
Debt Instrument [Line Items]
Aggregate Principal Committed		500,000		500,000
Outstanding Principal		386,465		416,395
Carrying Value		386,465		416,395	[1]
Fair Value		386,448	[2]	416,012	[3]
Unused Portion		113,535	[4]	83,605	[5]
Amount Available		113,535	[6]	82,813	[7]
Revolving Credit Facility
Debt Instrument [Line Items]
Aggregate Principal Committed		2,085,000		2,085,000
Outstanding Principal		383,871		976,462
Carrying Value		383,871		976,462	[1]
Fair Value		382,588	[2]	971,776	[3]
Unused Portion		1,701,129	[4]	1,108,538	[5]
Amount Available		1,701,129	[6]	722,012	[7]
December 2025 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed		62,000
Outstanding Principal		62,000
Carrying Value		60,932
Fair Value	[2]	60,932
January 2026 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed		38,000
Outstanding Principal		38,000
Carrying Value		37,307
Fair Value	[2]	37,307
December 2027 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed		82,000
Outstanding Principal		82,000
Carrying Value		79,673
Fair Value	[2]	79,673
January 2028 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed		18,000
Outstanding Principal		18,000
Carrying Value		17,472
Fair Value	[2]	17,472
September 2026 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed		226,000
Outstanding Principal		226,000
Carrying Value		223,605
Fair Value	[2]	223,605
September 2028 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed		325,000
Outstanding Principal		325,000
Carrying Value		318,680
Fair Value	[2]	318,680
September 2026 Euronotes
Debt Instrument [Line Items]
Aggregate Principal Committed		95,153
Outstanding Principal		95,153
Carrying Value		94,862
Fair Value	[2]	$ 94,862
2025 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed				62,000
Outstanding Principal				62,000
Carrying Value	[1]			61,964
Fair Value	[3]			61,964
2026 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed				38,000
Carrying Value	[1]			(105)
Unused Portion	[5]			38,000
2027 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed				82,000
Outstanding Principal				82,000
Carrying Value	[1]			81,769
Fair Value	[3]			81,769
2028 Notes
Debt Instrument [Line Items]
Aggregate Principal Committed				18,000
Carrying Value	[1]			(88)
Unused Portion	[5]			$ 18,000

[1] Negative values (if any) represent adjustments to debt valuation in connection with gain/losses on interest rate swap valuation on qualifying hedge accounting relationships. Please see Note 5 for additional details.

[2] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of September 30, 2023. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.

[3] The fair value of these debt obligations would be categorized as Level 3 under ASC 820 as of December 31, 2022. The valuation is based on a yield analysis and discount rate commensurate with the market yields for similar types of debt.

[4] The unused portion is the amount upon which commitment fees, if any, are based.

[5] The unused portion is the amount upon which commitment fees, if any, are based.

[6] The amount available reflects any limitations related to each respective credit facility’s borrowing base.

[7] The amount available reflects any limitations related to each respective credit facility’s borrowing base.