Derivative and Hedging Activities - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative [Line Items]
Notional amount	$ 3,562,865,000		$ 2,893,041,000
Additional amount in excess of posted collateral required in case of breached agreements	$ 1,600,000		1,300,000
Interest Rate Contracts [Member]
Derivative [Line Items]
Period to reclassification of cash flow hedge gain loss	12 months
Maximum length of time hedged in interest rate cash flow hedge	7 years
Derivative gains to be reclassified within twelve months	$ 1,600,000
Derivative gains to be reclassified within twelve months, net of tax	1,000,000
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
Credit Risk Contract Sold [Member]
Derivative [Line Items]
Notional amount	120,500,000
Maximum exposure under credit risk agreement assuming customer default	$ 400,000		$ 100,000
Credit Risk Contract Sold [Member] | Minimum [Member]
Derivative [Line Items]
Risk participation agreements, term	9 months
Credit Risk Contract Sold [Member] | Maximum [Member]
Derivative [Line Items]
Risk participation agreements, term	14 years