Fair Values of Assets and Liabilities (Summary of Changes in Level 3 Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Loans held-for- investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 11,007	$ 13,953	$ 10,280	$ 9,620
Net Income	54	47	(309)	169
Other comprehensive income (loss)	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(588)	(7,877)	(4,565)	(9,337)
Net transfers into/(out of) Level 3	1,659	6,490	6,726	12,161
Ending Balance	12,132	12,613	12,132	12,613
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	127,604	77,203	92,081	85,638
Net Income	5,948	9,704	41,471	1,269
Other comprehensive income (loss)	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	133,552	86,907	133,552	86,907
Derivative assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	22,570	58,433	48,091	2,631
Net Income	(7,958)	8,454	(33,479)	64,256
Other comprehensive income (loss)	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	14,612	66,887	14,612	66,887
Municipal Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	117,606	117,255	109,876	111,950
Net Income	0	0	0	0
Other comprehensive income (loss)	(757)	64	(3,199)	(1,731)
Purchases	875	3,221	19,038	16,093
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	(1,069)	(7,991)	(6,841)
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	117,724	119,471	117,724	119,471
U.S. Government agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	2,293	1,966	2,646
Net Income	0	0	(4)	0
Other comprehensive income (loss)	0	(7)	(24)	(46)
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	(157)	(1,938)	(471)
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	$ 0	$ 2,129	$ 0	$ 2,129