Borrowings - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May 31, 2013	May 14, 2013
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 518,700,000
Outstanding borrowings with FHLB	0	0
Outstanding short term letters of credit	55,000,000	35,000,000
Maturity date	Oct. 07, 2033
Liquidation amount of trust preferred security	$ 1,000
Redemption date	Jul. 07, 2013
Settlement date	Jul. 08, 2013
Redemption in securities	619,000
Loss on Trust Preferred Securities hedge	0	(1,866,000)	0
Amount of maintained federal fund lines of credit with correspondent banks	82,000,000	82,000,000
Amount of federal fund lines of credit with correspondent banks	0	0
Amount of federal fund line of credit with Federal Reserve Bank of Philadelphia	0	0
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Loss on Trust Preferred Securities hedge				1,900,000
Interest rate swap maturity date	Jan. 07, 2019
London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate					3.05%
Trust Preferred Securities [Member]
Debt Instrument [Line Items]
Aggregate principal balance of capital securities redeemed					20,000,000