Loans - Average Recorded Investment and Interest Income Recognized on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$ 220,288	$ 189,830	$ 218,853	$ 190,006
Interest Income Recognized	1,711	919	3,102	2,206
Commercial real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	133,998	119,489	133,282	116,746
Interest Income Recognized	936	339	1,756	1,077
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,174	274	1,194	277
Interest Income Recognized	14	3	26	7
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	56,017	48,888	55,644	52,094
Interest Income Recognized	412	339	788	748
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	114,066	98,077	113,735	95,004
Interest Income Recognized	866	302	1,617	991
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	19,932	21,412	19,547	21,742
Interest Income Recognized	70	37	139	86
Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	29,099	21,179	28,686	20,889
Interest Income Recognized	349	238	532	374
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,174	274	1,194	277
Interest Income Recognized	$ 14	$ 3	$ 26	$ 7