Borrowings - Cabot Securitisation Senior Facility (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2022	Jun. 30, 2023 USD ($)	Jun. 30, 2022	Jun. 30, 2023 GBP (£)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Book value	$ 4,876,570		$ 4,876,570			$ 4,508,360
United Kingdom, Pounds
Debt Instrument [Line Items]
Foreign currency exchange rate, translation	0.79		0.79		0.79
Cabot securitisation senior facility
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 443,800		$ 443,800		£ 350,000,000
Book value	$ 459,000		$ 459,000		£ 362,000,000
Weighted average interest rate (as a percent)	5.25%	3.95%	5.25%	3.70%
Cabot securitisation senior facility | Sterling Overnight Index Average (SONIA) | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			3.00%
Cabot securitisation senior facility | Minimum | Sterling Overnight Index Average (SONIA) | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			0.00%
Cabot securitisation senior facility | Maximum | Sterling Overnight Index Average (SONIA) | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			1.00%