Securitizations and Variable Interest Entities - Unconsolidated VIEs with Significant Continuing Involvement (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Maximum Exposure to Loss		$ 6,000
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	$ 4,529,346	2,368,339
Carrying Value, Net Assets	273,110	90,176
Maximum Exposure to Loss	273,110	147,190
Securities Available for Sale \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	220,135	116,768
Maximum Exposure to Loss	220,135	116,770
Accrued Interest Receivable \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	877	1,214
Maximum Exposure to Loss	877	1,214
Other Assets \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	52,098	29,206
Maximum Exposure to Loss	52,098	29,206
Accrued Expenses and Other Liabilities \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	0
Maximum Exposure to Loss	0	0
Securities Sold Under Repurchase Agreements \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	(57,012)
Maximum Exposure to Loss	0	0
Unconsolidated Trusts \| Accrued Expenses and Other Liabilities \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	0
Maximum Exposure to Loss	0	0
Unconsolidated Trusts \| Securities Sold Under Repurchase Agreements \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	(57,012)
Maximum Exposure to Loss	0	0
Certificate Program \| Accrued Expenses and Other Liabilities \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	0
Maximum Exposure to Loss	0	0
Certificate Program \| Securities Sold Under Repurchase Agreements \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	0
Maximum Exposure to Loss	0	0
Investment Fund \| Accrued Expenses and Other Liabilities \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	0
Maximum Exposure to Loss	0	0
Investment Fund \| Securities Sold Under Repurchase Agreements \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0	0
Maximum Exposure to Loss	0	0
Unconsolidated Trusts \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	1,909,219	1,359,367
Carrying Value, Net Assets	113,011	24,122
Maximum Exposure to Loss	113,011	81,135
Unconsolidated Trusts \| Securities Available for Sale \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	93,881	68,338
Maximum Exposure to Loss	93,881	68,339
Unconsolidated Trusts \| Accrued Interest Receivable \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	362	958
Maximum Exposure to Loss	362	958
Unconsolidated Trusts \| Other Assets \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	18,768	11,838
Maximum Exposure to Loss	18,768	11,838
Certificate Program \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	2,585,957	973,815
Carrying Value, Net Assets	152,357	57,801
Maximum Exposure to Loss	152,357	57,802
Certificate Program \| Securities Available for Sale \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	126,254	48,430
Maximum Exposure to Loss	126,254	48,431
Certificate Program \| Accrued Interest Receivable \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	515	256
Maximum Exposure to Loss	515	256
Certificate Program \| Other Assets \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	25,588	9,115
Maximum Exposure to Loss	25,588	9,115
Investment Fund \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	34,170	35,157
Carrying Value, Net Assets	7,742	8,253
Maximum Exposure to Loss	7,742	8,253
Investment Fund \| Securities Available for Sale \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	0	0
Maximum Exposure to Loss	0	0
Investment Fund \| Accrued Interest Receivable \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	0	0
Maximum Exposure to Loss	0	0
Investment Fund \| Other Assets \| Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	7,742	8,253
Maximum Exposure to Loss	$ 7,742	$ 8,253
Other Assets
Variable Interest Entity [Line Items]
Ownership (percent)	23.00%
Investment	$ 7,700

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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Net carrying amount of the assets and liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), when the reporting entity is not the VIE's primary beneficiary.

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Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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