Fair Values of Assets and Liabilities - Schedule of Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 33,054	$ 29,296	$ 30,419	$ 24,943
Total gains or losses included in earnings	0	77	105	77
Total gains or losses included in other comprehensive income	4,851	1,053	7,471	5,796
Purchases	0	0	500	0
Issuances	0	0	0	0
Sales	0	2,396	0	(3,112)
Settlements	464	775	(1,054)	(1,165)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	2,319	0	3,035
Balance, end of period	37,441	29,574	37,441	29,574
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	31,134	27,876	28,999	23,523
Total gains or losses included in earnings	0	0	105	0
Total gains or losses included in other comprehensive income	4,851	1,053	7,471	5,796
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	464	775	(1,054)	(1,165)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Balance, end of period	35,521	28,154	35,521	28,154
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,920	1,420	1,420	1,420
Total gains or losses included in earnings	0	0	0	0
Total gains or losses included in other comprehensive income	0	0	0	0
Purchases	0	0	500	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	0	0	0	0
Balance, end of period	$ 1,920	1,420	1,920	1,420
Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period		0		0
Total gains or losses included in earnings		77	$ 0	77
Total gains or losses included in other comprehensive income		0		0
Purchases		0		0
Issuances		0		0
Sales		2,396		(3,112)
Settlements		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		2,319		3,035
Balance, end of period		$ 0		$ 0