Loans - Average Recorded Investment and Interest Income Recognized on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$ 203,896	$ 170,658
Interest Income Recognized	5,103	6,350
Commercial real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	123,393	108,439
Interest Income Recognized	2,910	4,184
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	943	109
Interest Income Recognized	14	3
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	47,940	43,095
Interest Income Recognized	1,463	1,457
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	101,972	76,542
Interest Income Recognized	2,640	3,043
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	21,421	31,897
Interest Income Recognized	270	1,141
Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	31,620	19,015
Interest Income Recognized	716	706
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	943	109
Interest Income Recognized	$ 14	$ 3