Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 Category	Dec. 31, 2014	Mar. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of categories occupied under commercial real estate loans	2
Originated loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired TDRs Loans	45,641,000	$ 45,676,000	$ 56,179,000
Additional funds in TDRs	4,000	54,000	1,000
PNCI loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Impaired TDRs Loans	1,231,000	1,307,000	1,179,000
Obligations to lend additional funds on TDRs	0	$ 0	$ 0
Minimum [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Period of collateral payment of loan	3 months
Maximum [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Period of collateral payment of loan	12 months