Derivative and Hedging Activities - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Derivative [Line Items]
Notional amount	$ 2,751,532		$ 2,215,056
Derivative assets	66,293		45,898
Derivative liabilities	62,806		46,160
Amounts reclassified from AOCI	(1,793)
Additional amount in excess of posted collateral required in case of breached agreements	1,816		1,862
Interest Rate Contracts [Member]
Derivative [Line Items]
Notional amount	$ 250,000		200,000
Period to reclassification of cash flow hedge gain loss	12 months
Maximum length of time hedged in interest rate cash flow hedge	8 years
Derivative gains to be reclassified within twelve months	$ 2,219
Derivative gains to be reclassified within twelve months, net of tax	1,443
Derivative gain or loses excluded from assessment of hedge effectiveness	0
Hedge ineffectiveness	0	$ 0
Gains or losses from cash flow hedge derivatives reclassified to earnings	0	0
Interest Rate Contracts [Member] | Interest Income - Loans and Leases [Member]
Derivative [Line Items]
Derivative financial instrument, net	2,440	$ 2,479
Interest Rate Contracts [Member] | Interest Income - Loans and Leases [Member] | Amount Reclassified from Other Comprehensive Income [Member]
Derivative [Line Items]
Derivative financial instrument, net	2,440
Amounts reclassified from AOCI	1,586
Interest Rate Contracts [Member] | Interest Expense - Short-term Borrowings [Member]
Derivative [Line Items]
Derivative financial instrument, net	115
Interest Rate Contracts [Member] | Interest Expense - Short-term Borrowings [Member] | Amount Reclassified from Other Comprehensive Income [Member]
Derivative [Line Items]
Derivative financial instrument, net	115
Amounts reclassified from AOCI	75
Interest Rate Swap [Member]
Derivative [Line Items]
Notional amount	1,193,598		972,002
Credit Risk Contract Sold [Member]
Derivative [Line Items]
Notional amount	$ 74,010
Risk participation agreements, minimum term	2 years
Risk participation agreements, maximum term	9 years
Maximum exposure under credit risk agreement assuming customer default	$ 185		25
Trading Assets [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative assets	61,349		43,742
Not for Trading Assets [Member] | Interest Rate Contracts [Member]
Derivative [Line Items]
Derivative assets	4,918		2,109
Trading Liabilities [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative liabilities	61,754		43,783
Not for Trading Liabilities [Member] | Interest Rate Contracts [Member]
Derivative [Line Items]
Derivative liabilities	$ 855		$ 2,330