Investments - Allowance for Credit Loss on Beneficial Interests (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance	$ (2,959)	$ (6,959)	$ (4,453)	$ 0
Reclassification to/(from) non-credit discount from/(to) the allowance for changes in payment expectations	274	0	1,709	(2,553)
Increase in allowance for expected credit losses for acquisitions	(618)	(225)	(2,211)	(2,778)
Credit loss expense on beneficial interests	(85)	(141)	(440)	(570)
Reversal of allowance for expected credit losses due to increases in the net present value of expected cash flows	2,770	1,443	4,777	1,687
Allowance for expected credit losses, ending balance	(618)	(5,882)	(618)	(5,882)
Beginning period adjustment for CECL adoption
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Allowance for expected credit losses, beginning balance	$ 0	$ 0	$ 0	$ (1,668)