Loans Receivable and Allowance for Loan Losses - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) Commitment Loan	Mar. 31, 2015 USD ($) Loan	Dec. 31, 2015 USD ($) Commitment
Financing Receivable, Modifications [Line Items]
Funds for reimbursement	$ 1.4		$ 1.2
Loans reported as TDR	$ 14.0		$ 11.4
Minimum performance requirement (months)	6 months
Number of commitments to lend additional funds (commitment) | Commitment	0		0
Loans modified as TDR allowance	3	0
Loans receivable, covered	$ 13.2		$ 13.8
FDIC Loss Sharing Arrangement, clawback liability payment date (days)	45 days
FDIC Loss Sharing Arrangement, clawback liability	$ 2.4
FDIC Loss Sharing Arrangement, expected FDIC receivable	0.1
FDIC Loss Sharing Arrangement, clawback liability net of FDIC receivable	2.5
Residential real estate
Financing Receivable, Modifications [Line Items]
Residential real estate held in other real estate owned	1.2		1.2
Loans in process of foreclosure	$ 0.9		$ 0.6
Commercial and industrial
Financing Receivable, Modifications [Line Items]
Number of loans modified as TDR (loan) | Loan	2
Loans modified as TDR	$ 0.5
Loans modified as TDR allowance	2
Allowance for credit losses, effect of change in method	$ 0.2
Commercial real estate - non-owner occupied
Financing Receivable, Modifications [Line Items]
Number of loans modified as TDR (loan) | Loan	1
Loans modified as TDR	$ 0.2
Loans modified as TDR allowance	1
Allowance for credit losses, effect of change in method	$ 0.1
Manufactured housing
Financing Receivable, Modifications [Line Items]
Number of loans modified as TDR (loan) | Loan	36	6
Loans modified as TDR	$ 1.9	$ 0.5