Investment Securities - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Fair Value	$ 2,453,999	$ 1,989,439
Unrealized loss position for less than 12 months, Unrealized Loss	(67,367)	(9,419)
Unrealized loss position for more than 12 months, Fair Value	167,784	107,592
Unrealized loss position for more than 12 months, Unrealized Loss	$ (2,821)	$ (1,055)
Investment securities:
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Number of securities in loss position \| security	98	69
Unrealized loss position for more than 12 months, Number of securities in loss position \| security	20	24
Floating Interest Rate \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Fair Value	$ 0	$ 0
Unrealized loss position for less than 12 months, Unrealized Loss	0	0
Unrealized loss position for more than 12 months, Fair Value	18,961	19,254
Unrealized loss position for more than 12 months, Unrealized Loss	(690)	(394)
Floating Interest Rate \| Floating rate asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Fair Value		459,195
Unrealized loss position for less than 12 months, Unrealized Loss		(619)
Unrealized loss position for more than 12 months, Fair Value		37,307
Unrealized loss position for more than 12 months, Unrealized Loss		(477)
Floating Interest Rate \| Guaranteed mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Fair Value	707,266	406,805
Unrealized loss position for less than 12 months, Unrealized Loss	(2,751)	(5,730)
Unrealized loss position for more than 12 months, Fair Value	29,511	0
Unrealized loss position for more than 12 months, Unrealized Loss	(279)	0
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Fair Value	520,485
Unrealized loss position for less than 12 months, Unrealized Loss	(48,688)
Unrealized loss position for more than 12 months, Fair Value	0
Unrealized loss position for more than 12 months, Unrealized Loss	0
Fixed Interest Rate \| Fixed rate U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, Fair Value	1,226,248	1,123,439
Unrealized loss position for less than 12 months, Unrealized Loss	(15,928)	(3,070)
Unrealized loss position for more than 12 months, Fair Value	119,312	51,031
Unrealized loss position for more than 12 months, Unrealized Loss	$ (1,852)	$ (184)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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