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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Loans held-for- investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 26,620	$ 28,548	$ 33,717	$ 22,137
Net Income	(260)	1,304	(1,388)	1,192
Other comprehensive loss	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(16,402)	(2,159)	(22,657)	(5,491)
Net transfers into/(out of) Level 3	3,806	2,480	4,092	12,335
Ending Balance	13,764	30,173	13,764	30,173
Mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	54,572	21,596	33,676	19,103
Net Income	8,622	5,711	15,712	8,204
Other comprehensive loss		0		0
Purchases		0	13,806	0
Issuances	0	0	0	0
Settlements		0		0
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	63,194	27,307	63,194	27,307
Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	4,605	3,582	2,157	2,291
Net Income	(786)	(2,535)	1,662	(1,244)
Other comprehensive 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	3,819	1,047	3,819	1,047
Municipal Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	84,592	79,745	77,181	79,626
Net Income		0		0
Other comprehensive loss	(895)	2,572	(3,085)	3,029
Purchases	14,746	3,293	27,016	10,879
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(1,877)	(8,269)	(4,546)	(16,193)
Net transfers into/(out of) Level 3		0		0
Ending Balance	96,566	77,341	96,566	77,341
U.S. Government agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,616	4,283	3,779	0
Net Income	0	0	0	0
Other comprehensive loss	(134)	(173)	(297)	(173)
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	4,283
Ending Balance	$ 3,482	$ 4,110	$ 3,482	$ 4,110