Derivatives - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) Agreement	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Derivative [Line Items]
Termination value of derivatives in a net liability position	$ 20,800,000
Collateral obligations for derivative counterparties	23,700,000
Interest Income [Member] | Cash Flow Hedges [Member]
Derivative [Line Items]
Impact of derivative income reflected in income statement	$ 2,100,000	$ 300,000	$ 0
Interest Rate Swaps [Member]
Derivative [Line Items]
Number of interest rate swap agreements | Agreement	2
Interest Rate Swaps [Member] | Noninterest Income [Member]
Derivative [Line Items]
Impact of derivative income reflected in income statement	$ 2,700,000	$ 1,600,000	$ 4,700,000
Interest Rate Swaps [Member] | $300 Million Swap Agreement [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 300,000,000
Variable rate term loan agreement maturity	2017-01
Interest Rate Swaps [Member] | $200 Million Swap Agreement [Member]
Derivative [Line Items]
Notional amount of derivatives	$ 200,000,000
Variable rate term loan agreement maturity	2017-06