Fair Value of Assets and Liabilities - Fair Value Reconciliation (Detail) - Loans Invested in by Company - Loans Held For Sale - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Loans
Outstanding principal balance, beginning	$ 132,600	$ 747,394
Valuation adjustment, beginning	(10,698)	(25,039)
Fair value, beginning	121,902	722,355
Outstanding principal balance, purchases	7,507,695	1,568,844
Valuation adjustment, purchases	(1,629)	(6)
Fair value, purchases	7,506,066	1,568,838
Outstanding principal balance, transfers (to) from loans held for investment and/or loans held for sale		(41,431)
Valuation adjustment, transfers (to) from loans held for investment and/or loans held for sale		0
Fair value, transfers (to) from loans held for investment and/or loans held for sale		(41,431)
Outstanding principal balance, sales	(7,386,633)	(1,907,446)
Valuation adjustment, sales	5,124	87,723
Fair value, sales	(7,381,509)	(1,819,723)
Outstanding principal balance, principal payments and retirements	(98,530)	(207,483)
Valuation adjustment, principal payments and retirements	0	0
Fair value, principal payments and retirements	(98,530)	(207,483)
Outstanding principal balance, charge-offs, net of recoveries	(7,939)	(27,278)
Valuation adjustment, charge-offs, net of recoveries	3,441	25,627
Fair value, charge-offs, net of recoveries	(4,498)	(1,651)
Outstanding principal balance, change in fair value recorded in earnings	0	0
Valuation adjustment, change in fair value recorded in earnings	(1,061)	(99,003)
Fair value, change in fair value recorded in earnings	(1,061)	(99,003)
Outstanding principal balance, ending	147,193	132,600
Valuation adjustment, ending	(4,823)	(10,698)
Fair value, ending	$ 142,370	$ 121,902