Securities Available for Sale - Amortized Cost/Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 872,341	$ 399,668
Gross Unrealized Gains	4,574	9,424
Gross Unrealized Losses	(81,246)	(63,390)
Fair Value	795,669	345,702
Assets pledged as collateral
Debt Securities, Available-for-sale [Line Items]
Fair Value	341,600	319,000
Senior asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	413,850
Gross Unrealized Gains	0
Gross Unrealized Losses	(1,453)
Fair Value	412,397
U.S. agency residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	263,568	255,675
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(52,331)	(41,248)
Fair Value	211,237	214,427
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	93,451	90,447
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(18,372)	(16,053)
Fair Value	75,079	74,394
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	43,162	26,988
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7,013)	(4,470)
Fair Value	36,149	22,518
Other asset-backed securities related to Structured Program transactions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,831
Gross Unrealized Gains	4,540
Gross Unrealized Losses	(309)
Fair Value	31,062
Restricted investments	24,800
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	28,217	14,959
Gross Unrealized Gains	34	29
Gross Unrealized Losses	(787)	(785)
Fair Value	27,464	14,203
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,262	3,277
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(981)	(834)
Fair Value	$ 2,281	$ 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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