Investments - Narrative (Details) - USD ($)			3 Months Ended		9 Months Ended
		Jan. 01, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Gross unrealized gains			$ 3,600,000		$ 3,600,000		$ 1,200,000
Gross unrealized loss			200,000		200,000		800,000
Investment In securities			54,700,000	$ 83,400,000	287,600,000	$ 144,700,000
Provision for credit losses		$ 10,200,000
Financial Asset, Past Due
Debt Securities, Available-for-sale [Line Items]
Securities past due			0		0		0
Beneficial interests in securitization trusts
Debt Securities, Available-for-sale [Line Items]
Provision for credit losses		$ (1,700,000)
Reversal of provision for credit losses			2,800,000	1,400,000	4,800,000	1,700,000
Beneficial interests in securitization trusts
Debt Securities, Available-for-sale [Line Items]
Investment in beneficial interests			3,200,000	12,200,000	42,700,000	19,300,000
Senior notes
Debt Securities, Available-for-sale [Line Items]
Investment in senior notes			43,200,000	66,000,000	213,100,000	115,600,000
Subordinated debt
Debt Securities, Available-for-sale [Line Items]
Investment in subordinate notes			8,300,000	$ 5,200,000	31,800,000	$ 9,800,000
Beneficial interests in securitization trusts
Debt Securities, Available-for-sale [Line Items]
Gross unrealized gains			0		0		0
Gross unrealized loss			0		0		0
Carrying value	[1]		$ 139,494,000		$ 139,494,000		$ 91,418,000

[1] Investments in beneficial interests includes allowance for expected credit losses of $0.6 million and $4.5 million at September 30, 2021 and December 31, 2020, respectively.