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Securities Available for Sale - Schedule of Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value of AFS Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,565,829		$ 3,492,264
Gross Unrealized Gains	22,768		30,469
Gross Unrealized Losses	(57,426)		(66,558)
Allowance for Credit Losses	(4,029)		(3,527)
Fair Value	3,527,142		3,452,648
Senior asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,940,007		2,870,071
Gross Unrealized Gains	22,468		30,398
Gross Unrealized Losses	0		(645)
Allowance for Credit Losses	0		0
Fair Value	2,962,475		2,899,824
Portfolio layer method basis adjustment - increase (decrease)	45		(2,200)
U.S. agency residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	265,088		270,120
Gross Unrealized Gains	164		48
Gross Unrealized Losses	(37,635)		(43,243)
Allowance for Credit Losses	0		0
Fair Value	227,617		226,925
Other asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	188,831		174,132
Gross Unrealized Gains	40		0
Gross Unrealized Losses	(810)		(657)
Allowance for Credit Losses	(4,029)	$ (4,848)	(3,527)	$ (2,083)	$ (2,892)	$ 0
Fair Value	184,032		169,948
Restricted investments	181,300		169,900
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	87,461		90,459
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(12,327)		(14,513)
Allowance for Credit Losses	0		0
Fair Value	75,134		75,946
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	61,945		62,882
Gross Unrealized Gains	47		8
Gross Unrealized Losses	(5,439)		(6,216)
Allowance for Credit Losses	0		0
Fair Value	56,553		56,674
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19,271		21,364
Gross Unrealized Gains	49		15
Gross Unrealized Losses	(449)		(587)
Allowance for Credit Losses	0		0
Fair Value	18,871		20,792
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,226		3,236
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(766)		(697)
Allowance for Credit Losses	0		0
Fair Value	$ 2,460		$ 2,539