Loans - Average Recorded Investment and Interest Income Recognized on Impaired Loans by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	$ 46,885	$ 37,965	$ 47,152	$ 38,577
Interest Income Recognized	112	137	334	297
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	10,606	1,354	6,665	458
Interest Income Recognized	38	1	58	1
Commercial real estate: Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	0	94	0	101
Interest Income Recognized	0	0	0	0
Commercial real estate: Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	20,954	20,539	25,413	20,693
Interest Income Recognized	45	113	200	229
Residential: 1-4 family [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	14,092	15,366	14,285	16,603
Interest Income Recognized	18	19	58	56
Residential: Home equities [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	1,233	610	789	721
Interest Income Recognized	11	4	18	11
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Average Recorded Investment	0	2	0	1
Interest Income Recognized	$ 0	$ 0	$ 0	$ 0