Securitizations and Variable Interest Entities - Unconsolidated VIEs with Significant Continuing Involvement (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 4,750,760	$ 1,863,293
Investment Fund
Variable Interest Entity [Line Items]
Assets	1,731,267	3,233,416
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Assets	93,426	174,891
Net Assets	93,426	174,891
Maximum Exposure to Loss	93,426	174,891
Unconsolidated Trusts | Investment Fund
Variable Interest Entity [Line Items]
Assets	763,992	1,267,611
Unconsolidated Trusts | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	36,770	67,165
Maximum Exposure to Loss	36,770	67,165
Certificate Program | Investment Fund
Variable Interest Entity [Line Items]
Assets	929,742	1,931,429
Certificate Program | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	48,931	99,951
Maximum Exposure to Loss	48,931	99,951
Investment Fund | Investment Fund
Variable Interest Entity [Line Items]
Assets	37,533	34,376
Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	7,725	7,775
Maximum Exposure to Loss	7,725	7,775
Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	73,694	142,026
Maximum Exposure to Loss	73,694	142,026
Securities Available for Sale | Unconsolidated Trusts | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	31,253	57,511
Maximum Exposure to Loss	31,253	57,511
Securities Available for Sale | Certificate Program | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	42,441	84,515
Maximum Exposure to Loss	42,441	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	19,732	32,865
Maximum Exposure to Loss	19,732	32,865
Other Assets | Unconsolidated Trusts | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	5,517	9,654
Maximum Exposure to Loss	5,517	9,654
Other Assets | Certificate Program | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	6,490	15,436
Maximum Exposure to Loss	6,490	15,436
Other Assets | Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Net Assets	7,725	7,775
Maximum Exposure to Loss	$ 7,725	$ 7,775
Other Assets
Variable Interest Entity [Line Items]
Ownership (percent)	21.00%
Other assets	$ 7,700