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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Loans held-for- investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 9,568	$ 11,249	$ 9,620	$ 11,347
Net Income	200	118	122	285
Other comprehensive income (loss)	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(1,364)	(886)	(1,460)	(1,351)
Net transfers into/(out of) Level 3	5,549	0	5,671	200
Ending Balance	13,953	10,481	13,953	10,481
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	73,504	71,022	85,638	75,183
Net Income	3,699	1,421	(8,435)	(2,740)
Other comprehensive income (loss)	0	0	0	0
Purchases	0	407	0	407
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	77,203	72,850	77,203	72,850
Derivative Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	39,816	3,089	2,631	2,457
Net Income	18,617	507	55,802	1,139
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	58,433	3,596	58,433	3,596
Municipal Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	113,267	103,834	111,950	108,926
Net Income	0	0	0	0
Other comprehensive income (loss)	(546)	6,519	(1,795)	8,056
Purchases	6,997	555	12,872	1,524
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(2,463)	(612)	(5,772)	(8,210)
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	117,255	110,296	117,255	110,296
U.S. Government agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,457	2,993	2,646	3,150
Net Income	0	0	0	0
Other comprehensive income (loss)	(7)	142	(39)	143
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(157)	(158)	(314)	(316)
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	$ 2,293	$ 2,977	$ 2,293	$ 2,977