Significant Accounting Policies and Basis of Presentation - Narrative (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) Segment CompensationPlan	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)
Derivative [Line Items]
Average reserve balances maintained with federal reserve bank	$ 73,200,000	$ 61,200,000
Deferred cost of bank loans	$ 0
Contractual payment of principal duration (days)	90 days
Contractual terms for loans (months)	6 months
Covered loans outstanding	$ 13,800,000	42,200,000
Maximum loan to value ratio	80.00%
Delinquency period for loan charge-offs (days)	120 days
Goodwill	$ 3,651,000	3,664,000
FHLB, Federal Reserve Bank, and other restricted stock	90,841,000	82,002,000
Federal Home Loan Bank stock	$ 78,900,000	71,600,000
Clawback liability payment date	45 days
Clawback liability	$ 2,300,000
Expected FDIC receivable	200,000
Clawback liability, net	$ 2,100,000
Percentage of tax position will realized or sustained upon examination	50.00%
Number of share-based compensation plans | CompensationPlan	4
Number of reportable segments (segment) | Segment	1
Interest Rate Swap | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative notional amount	$ 461,000,000.0	251,900,000.0
Interest Rate Swap | Cash Flow Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Derivative notional amount	150,000,000.0	150,000,000.0	$ 150,000,000
Credit contracts | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative notional amount	$ 19,300,000.0	13,400,000.0	$ 19,300,000
ESPP
Derivative [Line Items]
Purchase price under employee stock purchase plan (percent)	85.00%
Purchase price under employee stock purchase plan, discount (percent)	15.00%
Federal Deposit Insurance Corporation
Repurchase Agreement Counterparty [Line Items]
Other real estate owned	$ 500,000	$ 9,400,000