Securities Available for Sale - Amortized cost/fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,663,990	$ 399,668
Gross Unrealized Gains	13,896	9,424
Gross Unrealized Losses	(57,624)	(63,390)
Fair Value	1,620,262	345,702
Asset Pledged as Collateral
Debt Securities, Available-for-sale [Line Items]
Fair Value	359,500	319,000
Senior asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,165,513
Gross Unrealized Gains	10,932
Gross Unrealized Losses	(42)
Fair Value	1,176,403
U.S. agency residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	261,885	255,675
Gross Unrealized Gains	208	0
Gross Unrealized Losses	(37,497)	(41,248)
Fair Value	224,596	214,427
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	93,452	90,447
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(13,348)	(16,053)
Fair Value	80,104	74,394
Other asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	70,662
Gross Unrealized Gains	2,731
Gross Unrealized Losses	0
Fair Value	73,393
Restricted investments	70,100
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	42,511	26,988
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5,435)	(4,470)
Fair Value	37,076	22,518
Asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		8,322
Gross Unrealized Gains		9,395
Gross Unrealized Losses		0
Fair Value		17,717
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,710	14,959
Gross Unrealized Gains	25	29
Gross Unrealized Losses	(634)	(785)
Fair Value	26,101	14,203
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,257	3,277
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(668)	(834)
Fair Value	$ 2,589	$ 2,443

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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