Financial Guarantees - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Financial Guarantees [Line Items]
Term of standby letters of credit, years	1 year
Notional amount of standby letters of credit	$ 60,000,000	$ 65,300,000
Carrying value of letters of credit	400,000	400,000
Interest rate swap, notional amount	708,000,000	608,000,000
Interest Rate Swap [Member]
Financial Guarantees [Line Items]
Interest rate swap, notional amount	7,600,000
Interest Rate Swap [Member] | Additional Risk Participation [Member]
Financial Guarantees [Line Items]
Interest rate swap, notional amount	$ 13,200,000