Loans - Average Recorded Investment and Interest Income Recognized on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	$ 217,307	$ 190,183
Interest Income Recognized	1,391	1,287
Commercial real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	132,559	113,973
Interest Income Recognized	820	738
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,214	279
Interest Income Recognized	12	4
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	55,266	55,336
Interest Income Recognized	376	409
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	113,401	91,897
Interest Income Recognized	751	689
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	19,158	22,076
Interest Income Recognized	69	49
Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	28,268	20,595
Interest Income Recognized	183	136
Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average Recorded Investment	1,214	279
Interest Income Recognized	$ 12	$ 4