Securitizations and Variable Interest Entities - Unconsolidated VIEs with Significant Continuing Involvement (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 4,370,101	$ 1,863,293
Investment Fund
Variable Interest Entity [Line Items]
Assets	2,170,259	3,233,416
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Assets	118,482	174,891
Net Assets	118,482	174,891
Maximum Exposure to Loss	118,482	174,891
Unconsolidated Trusts | Investment Fund
Variable Interest Entity [Line Items]
Assets	920,791	1,267,611
Unconsolidated Trusts | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	46,406	67,165
Maximum Exposure to Loss	46,406	67,165
Certificate Program | Investment Fund
Variable Interest Entity [Line Items]
Assets	1,213,360	1,931,429
Certificate Program | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	64,301	99,951
Maximum Exposure to Loss	64,301	99,951
Investment Fund | Investment Fund
Variable Interest Entity [Line Items]
Assets	36,108	34,376
Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	7,775	7,775
Maximum Exposure to Loss	7,775	7,775
Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	95,474	142,026
Maximum Exposure to Loss	95,474	142,026
Securities Available for Sale | Unconsolidated Trusts | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	39,816	57,511
Maximum Exposure to Loss	39,816	57,511
Securities Available for Sale | Certificate Program | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	55,658	84,515
Maximum Exposure to Loss	55,658	84,515
Securities Available for Sale | Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	0	0
Maximum Exposure to Loss	0	0
Other Assets | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	23,008	32,865
Maximum Exposure to Loss	23,008	32,865
Other Assets | Unconsolidated Trusts | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	6,590	9,654
Maximum Exposure to Loss	6,590	9,654
Other Assets | Certificate Program | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	8,643	15,436
Maximum Exposure to Loss	8,643	15,436
Other Assets | Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	7,775	7,775
Maximum Exposure to Loss	$ 7,775	$ 7,775
Other Assets
Variable Interest Entity [Line Items]
Ownership (percent)	22.00%
Other assets	$ 7,800