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Securities Available for Sale - Amortized cost/fair value (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 272,909		$ 159,164
Gross Unrealized Gains	7,139		2,771
Gross Unrealized Losses	(1,951)		(973)
Allowance for Credit Losses	(592)	$ (914)	(18,736)	$ (15,571)	$ (18,835)	$ 0
Fair Value	277,505		142,226
Securities pledged as collateral at fair value	87,500		133,500
U.S. agency residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	93,945
Gross Unrealized Gains	106
Gross Unrealized Losses	(1,033)
Allowance for Credit Losses	0
Fair Value	93,018
Asset-backed senior securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	49,480		75,332
Gross Unrealized Gains	75		67
Gross Unrealized Losses	0		(27)
Allowance for Credit Losses	0		0
Fair Value	49,555		75,372
Securities pledged as collateral at fair value	236,700		133,500
CLUB Certificate asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	30,304		54,525
Gross Unrealized Gains	1,961		576
Gross Unrealized Losses	(68)		(772)
Allowance for Credit Losses	(40)	(48)	(4,190)	(6,587)	(8,638)	0
Fair Value	32,157		50,139
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31,422
Gross Unrealized Gains	28
Gross Unrealized Losses	(259)
Allowance for Credit Losses	0
Fair Value	31,191
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	28,655
Gross Unrealized Gains	216
Gross Unrealized Losses	(25)
Allowance for Credit Losses	0
Fair Value	28,846		200
U.S. agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,006
Gross Unrealized Gains	21
Gross Unrealized Losses	(554)
Allowance for Credit Losses	0
Fair Value	25,473
Asset-backed subordinated securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,590		29,107
Gross Unrealized Gains	4,723		2,128
Gross Unrealized Losses	0		(174)
Allowance for Credit Losses	(552)	$ (866)	(14,546)	$ (8,984)	$ (10,197)	$ 0
Fair Value			16,515
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,307
Gross Unrealized Gains	9
Gross Unrealized Losses	(12)
Allowance for Credit Losses	0
Fair Value	3,304
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	200		200
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Allowance for Credit Losses	0		0
Fair Value	200		200
Asset-backed securities, securitized loans and receivables, subject to restrictions on transfer
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 69,500		$ 119,300