Quarterly Financial Data (unaudited) - Error Corrections and Prior Period Adjustments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2020	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in finance receivables	$ 17,772	$ 83,955	$ 86,135	$ 70,505	$ 29,171	$ 38,453
Net cash provided by operating activities: continuing operations	(29,550)	124,845	229,589	339,884	258,611	352,568
Net cash from operating activities	(67,355)	86,422	191,166	301,972	267,883	344,652
Purchases of investment securities	(107,312)	(282,065)	(591,304)	(596,841)	(137,194)	(82,153)
Proceeds from sales/maturities of investment securities	104,222	214,466	501,459	576,536	108,548	175,866
Net change in short-term and other investing activities	0	0	0		0	0
Net investment in loan receivables	1,071	(387)	3,806		15,676	1,773
Customer deposits at the Bank	0	0	0		0	0
Other investing activities	8,081	1,539	9,559	4,636	(8,905)	8,168
Net cash from investing activities: continuing operations	(20,997)	(73,987)	(113,239)	(73,190)	(212,580)	(48,186)
Net cash from investing activities	(23,499)	(76,489)	(115,741)	(75,692)	457,550	286,346
Increase in customer deposits at the Bank	(888)	22,331	19,464	26,082	16,341	21,008
Net cash from financing activities	(160,484)	(62,267)	(197,908)	$ (235,371)	(670,299)	(745,411)
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in finance receivables	18,843	84,342	85,593		25,638	53,280
Net cash provided by operating activities: continuing operations	(28,479)	125,232	229,047		242,935	350,795
Net cash from operating activities	(66,284)	86,809	190,624		252,207	342,879
Purchases of investment securities	(67,312)	(115,565)	(392,427)		(57,194)	(81,527)
Proceeds from sales/maturities of investment securities	24,102	94,425	241,924		108,548	175,820
Net change in short-term and other investing activities	48,431	(44,035)	68,464		(78,814)	11,838
Net investment in loan receivables	0	0	0
Customer deposits at the Bank	(888)	22,331	19,464		16,341	21,008
Other investing activities	(230)	(885)	(1,511)		(10,091)	(4,250)
Net cash from investing activities: continuing operations	(22,956)	(52,043)	(93,233)		(180,563)	(25,405)
Net cash from investing activities	(25,458)	(54,545)	(95,735)		489,567	309,127
Increase in customer deposits at the Bank	0	0	0
Net cash from financing activities	(159,596)	(84,598)	(217,372)		(686,640)	(766,419)
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in finance receivables	(1,071)	(387)	542		15,676	1,773
Net cash provided by operating activities: continuing operations	(1,071)	(387)	542		15,676	1,773
Net cash from operating activities	(1,071)	(387)	542		15,676	1,773
Purchases of investment securities	(40,000)	(166,500)	(198,877)		(80,000)	(626)
Proceeds from sales/maturities of investment securities	80,120	120,041	259,535		0	46
Net change in short-term and other investing activities	(48,431)	44,035	(68,464)		78,814	(11,838)
Net investment in loan receivables	1,071	(387)	542		15,676	1,773
Customer deposits at the Bank	888	(22,331)	(19,464)		(16,341)	(21,008)
Other investing activities	8,311	2,424	7,806		1,186	12,418
Net cash from investing activities: continuing operations	1,959	(21,944)	(20,006)		(32,017)	(22,781)
Net cash from investing activities	1,959	(21,944)	(20,006)		(32,017)	(22,781)
Increase in customer deposits at the Bank	(888)	22,331	19,464		16,341	21,008
Net cash from financing activities	$ (888)	$ 22,331	19,464		16,341	21,008
Reclass
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Decrease in finance receivables					$ (12,143)	$ (16,600)
Net investment in loan receivables			3,264
Other investing activities			$ 3,264