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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Loans held-for- investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 28,548	$ 0	$ 22,137	$ 0
Total net gains (losses) included in Net income	1,304	0	1,192	0
Total net gains (losses) included in Other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(2,159)	0	(5,491)	0
Net transfers into/(out of) Level 3	2,480	0	12,335	0
Ending Balance	30,173	0	30,173	0
Mortgage Servicing Rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	21,596	10,128	19,103	9,092
Total net gains (losses) included in Net income	5,711	3,254	8,204	4,290
Total net gains (losses) included in Other comprehensive income		0		0
Purchases		0		0
Issuances	0	0	0	0
Settlements		0		0
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	27,307	13,382	27,307	13,382
Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	3,582	9,917	2,291	7,021
Total net gains (losses) included in Net income	(2,535)	(186)	(1,244)	2,710
Total net gains (losses) included in Other comprehensive income	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	1,047	9,731	1,047	9,731
Municipal Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	79,745	70,242	79,626	68,613
Total net gains (losses) included in Net income		0		0
Total net gains (losses) included in Other comprehensive income	2,572	113	3,029	100
Purchases	3,293	1,003	10,879	4,274
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(8,269)	(1,546)	(16,193)	(3,175)
Net transfers into/(out of) Level 3		0		0
Ending Balance	77,341	69,812	77,341	69,812
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	24,054	0	25,199
Total net gains (losses) included in Net income		0		0
Total net gains (losses) included in Other comprehensive income	0	1,133	0	(12)
Purchases		0		0
Issuances	0	0	0	0
Settlements		0		0
Net transfers into/(out of) Level 3	0	0	0	0
Ending Balance	0	25,187	0	25,187
U.S. Government agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	4,283	0	0	0
Total net gains (losses) included in Net income	0	0	0	0
Total net gains (losses) included in Other comprehensive income	(173)	0	(173)	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	4,283	0
Ending Balance	$ 4,110	$ 0	$ 4,110	$ 0