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, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	$ 24,943	$ 24,793
Total gains or losses included in earnings	77	(770)
Total gains or losses included in other comprehensive income	7,162	12,338
Purchases	0	0
Issuances	0	0
Sales	(3,112)	(20,760)
Settlements	(1,686)	(10,793)
Transfers from Level 3	0	0
Transfers into Level 3	3,035	20,135
Balance, end of period	30,419	24,943
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	23,523	23,373
Total gains or losses included in earnings	0	(1,395)
Total gains or losses included in other comprehensive income	7,162	12,338
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	(1,686)	(10,793)
Transfers from Level 3	0	0
Transfers into Level 3	0	0
Balance, end of period	28,999	23,523
Equities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	1,420	1,420
Total gains or losses included in earnings	0	0
Total gains or losses included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Transfers from Level 3	0	0
Transfers into Level 3	0	0
Balance, end of period	1,420	1,420
Loans Held for Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	0	0
Total gains or losses included in earnings	77	625
Total gains or losses included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	(3,112)	(20,760)
Settlements	0	0
Transfers from Level 3	0	0
Transfers into Level 3	3,035	20,135
Balance, end of period	0	0
Other Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of period	0	0
Total gains or losses included in earnings	0	0
Total gains or losses included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Transfers from Level 3	0	0
Transfers into Level 3	0	0
Balance, end of period	$ 0	$ 0