Fair Value of Assets and Liabilities - Fair Value Reconciliation (Detail) - Loans Invested in by Company - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Loans Held For Sale
Loans
Outstanding Principal Balance, Beginning	$ 174,130	$ 835,557	$ 132,600	$ 747,394
Valuation Adjustment, Beginning	(7,507)	(93,853)	(10,698)	(25,039)
Fair Value, Beginning	166,623	741,704	121,902	722,355
Outstanding Principal Balance, Purchases	2,038,450	23,363	2,980,395	1,402,457
Valuation Adjustment, Purchases	0	0	(1,629)	0
Fair Value, Purchases	2,038,450	23,363	2,978,766	1,402,457
Outstanding Principal Balance, Transfers (to) from loans held for investment and/or loans held for sale	1,244	(36)	1,181	(43,159)
Valuation Adjustment, Transfers (to) from loans to loans held for sale	0	0	0	0
Fair Value, Transfers (to) from loans to loans held for sale	1,244	(36)	1,181	(43,159)
Outstanding Principal Balance, Sales	(1,996,154)	(112,527)	(2,869,826)	(1,283,934)
Valuation Adjustment, Sales	3,616	10,947	10,653	30,856
Fair Value, Sales	(1,992,538)	(101,580)	(2,859,173)	(1,253,078)
Outstanding Principal Balance, Principal payments and retirements	(28,914)	(71,588)	(51,735)	(141,691)
Valuation Adjustment, Principal payments and retirements	0	0	0	0
Fair Value, Principal payments and retirements	(28,914)	(71,588)	(51,735)	(141,691)
Outstanding Principal Balance, Charge-offs, net of recoveries	(1,768)	(6,507)	(5,627)	(12,805)
Valuation Adjustment, Charge-offs, net of recoveries	734	6,018	3,920	11,797
Fair Value, Charge-offs, net of recoveries	(1,034)	(489)	(1,707)	(1,008)
Outstanding Principal Balance, Change in fair value recorded in earnings	0	0	0	0
Valuation Adjustment, Change in fair value recorded in earnings	(3,770)	(4,281)	(9,173)	(98,783)
Fair Value, Change in fair value recorded in earnings	(3,770)	(4,281)	(9,173)	(98,783)
Outstanding Principal Balance, Ending	186,988	668,262	186,988	668,262
Valuation Adjustment, Ending	(6,927)	(81,169)	(6,927)	(81,169)
Fair Value, Ending	180,061	587,093	180,061	587,093
Loans Held for Investment
Loans
Outstanding Principal Balance, Beginning	536,875	990,662	679,903	1,148,888
Valuation Adjustment, Beginning	(29,718)	(105,249)	(43,217)	(69,573)
Fair Value, Beginning	507,157	885,413	636,686	1,079,315
Outstanding Principal Balance, Purchases		55,274		159,894
Valuation Adjustment, Purchases		0		0
Fair Value, Purchases		55,274		159,894
Outstanding Principal Balance, Transfers (to) from loans held for investment and/or loans held for sale		(101)		(17,579)
Valuation Adjustment, Transfers (to) from loans to loans held for sale		0		0
Fair Value, Transfers (to) from loans to loans held for sale		(101)		(17,579)
Outstanding Principal Balance, Issuance		0		0
Valuation Adjustment, Issuances		0		0
Fair Value, Issuances		0		0
Outstanding Principal Balance, Principal payments and retirements	(114,739)	(171,541)	(245,759)	(387,289)
Valuation Adjustment, Principal payments and retirements	0	0	0	0
Fair Value, Principal payments and retirements	(114,739)	(171,541)	(245,759)	(387,289)
Outstanding Principal Balance, Charge-offs, net of recoveries	(8,201)	(22,818)	(20,209)	(52,438)
Valuation Adjustment, Charge-offs, net of recoveries	2,443	14,202	7,183	31,513
Fair Value, Charge-offs, net of recoveries	(5,758)	(8,616)	(13,026)	(20,925)
Outstanding Principal Balance, Change in fair value recorded in earnings	0	0	0	0
Valuation Adjustment, Change in fair value recorded in earnings	4,702	24,799	13,461	(28,188)
Fair Value, Change in fair value recorded in earnings	4,702	24,799	13,461	(28,188)
Outstanding Principal Balance, Ending	413,935	851,476	413,935	851,476
Valuation Adjustment, Ending	(22,573)	(66,248)	(22,573)	(66,248)
Fair Value, Ending	391,362	785,228	391,362	785,228
Notes, Certificates and Secured Borrowings
Loans
Outstanding Principal Balance, Beginning	536,875	990,662	679,903	1,148,888
Valuation Adjustment, Beginning	(29,672)	(103,822)	(43,129)	(67,422)
Fair Value, Beginning	507,203	886,840	636,774	1,081,466
Outstanding Principal Balance, Purchases		0		0
Valuation Adjustment, Purchases		0		0
Fair Value, Purchases		0		0
Outstanding Principal Balance, Transfers (to) from loans held for investment and/or loans held for sale		0		0
Valuation Adjustment, Transfers (to) from loans to loans held for sale		0		0
Fair Value, Transfers (to) from loans to loans held for sale		0		0
Outstanding Principal Balance, Issuance		55,274		159,894
Valuation Adjustment, Issuances		0		0
Fair Value, Issuances		55,274		159,894
Outstanding Principal Balance, Principal payments and retirements	(114,739)	(171,642)	(245,759)	(404,868)
Valuation Adjustment, Principal payments and retirements	0	0	0	0
Fair Value, Principal payments and retirements	(114,739)	(171,642)	(245,759)	(404,868)
Outstanding Principal Balance, Charge-offs, net of recoveries	(8,201)	(22,818)	(20,209)	(52,438)
Valuation Adjustment, Charge-offs, net of recoveries	2,398	13,556	7,050	29,987
Fair Value, Charge-offs, net of recoveries	(5,803)	(9,262)	(13,159)	(22,451)
Outstanding Principal Balance, Change in fair value recorded in earnings	0	0	0	0
Valuation Adjustment, Change in fair value recorded in earnings	4,723	24,718	13,528	(28,113)
Fair Value, Change in fair value recorded in earnings	4,723	24,718	13,528	(28,113)
Outstanding Principal Balance, Ending	413,935	851,476	413,935	851,476
Valuation Adjustment, Ending	(22,551)	(65,548)	(22,551)	(65,548)
Fair Value, Ending	391,384	785,928	391,384	785,928
Other Loans Held For Investment
Loans
Outstanding Principal Balance, Beginning	47,155	83,650	56,388	47,042
Valuation Adjustment, Beginning	(4,670)	(12,647)	(6,434)	(3,349)
Fair Value, Beginning	42,485	71,003	49,954	43,693
Outstanding Principal Balance, Purchases	39	386	155	1,113
Valuation Adjustment, Purchases	27	(312)	(71)	(1,005)
Fair Value, Purchases	66	74	84	108
Outstanding Principal Balance, Transfers (to) from loans held for investment and/or loans held for sale		137		43,325
Valuation Adjustment, Transfers (to) from loans to loans held for sale		0		0
Fair Value, Transfers (to) from loans to loans held for sale		137		43,325
Outstanding Principal Balance, Principal payments and retirements	(8,246)	(7,949)	(16,570)	(13,633)
Valuation Adjustment, Principal payments and retirements	0	0	0	0
Fair Value, Principal payments and retirements	(8,246)	(7,949)	(16,570)	(13,633)
Outstanding Principal Balance, Charge-offs, net of recoveries	(811)	(1,065)	(1,836)	(2,688)
Valuation Adjustment, Charge-offs, net of recoveries	755	377	1,329	511
Fair Value, Charge-offs, net of recoveries	(56)	(688)	(507)	(2,177)
Outstanding Principal Balance, Change in fair value recorded in earnings	0	0	0	0
Valuation Adjustment, Change in fair value recorded in earnings	274	2,980	1,562	(5,759)
Fair Value, Change in fair value recorded in earnings	274	2,980	1,562	(5,759)
Outstanding Principal Balance, Ending	38,137	75,159	38,137	75,159
Valuation Adjustment, Ending	(3,614)	(9,602)	(3,614)	(9,602)
Fair Value, Ending	$ 34,523	$ 65,557	$ 34,523	$ 65,557