Securities Available for Sale - Amortized cost/fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	$ 271,173	$ 170,189
Gross Unrealized Gains	1,078	588
Gross Unrealized Losses	(1,324)	(308)
Fair Value	270,927	170,469
Asset-backed senior securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	108,780	56,363
Gross Unrealized Gains	597	188
Gross Unrealized Losses	(38)	(62)
Fair Value	109,339	56,489
CLUB Certificate asset-backed securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	90,728	48,505
Gross Unrealized Gains	41	150
Gross Unrealized Losses	(1,063)	(225)
Fair Value	89,706	48,430
Asset-backed subordinated securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	20,888	11,602
Gross Unrealized Gains	423	249
Gross Unrealized Losses	(221)	(2)
Fair Value	21,090	11,849
Corporate debt securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	14,333	17,339
Gross Unrealized Gains	11	1
Gross Unrealized Losses	(1)	(12)
Fair Value	14,343	17,328
Certificates of deposit
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	13,100	14,929
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	13,100	14,929
Other asset-backed securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	12,075	11,232
Gross Unrealized Gains	6	0
Gross Unrealized Losses	(1)	(7)
Fair Value	12,080	11,225
Commercial paper
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	9,274	9,720
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	9,274	9,720
U.S. agency securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost	1,995
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	1,995
Other securities
Schedule of Securities Available-for-Sale [Line Items]
Amortized Cost		499
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		499
Asset-backed securities related to structured program transactions
Schedule of Securities Available-for-Sale [Line Items]
Fair Value	219,000	115,100
Assets Sold under Repurchase Agreements
Schedule of Securities Available-for-Sale [Line Items]
Securities pledged as collateral	$ 174,800	64,100
Securitized asset-backed senior securities
Schedule of Securities Available-for-Sale [Line Items]
Securities pledged as collateral		$ 53,600

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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