Loans and Allowance for Loan Losses - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment					$ 43,110
Recorded Investment, Total	26,829		26,829		33,592
Unpaid Principal Balance, Total	35,050		35,050
Related Allowance, Total	2,596		2,596		3,932
Average Recorded Balance, Total	28,080	47,817	30,238	39,130
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	6,168		6,168		12,585
Unpaid Principal Balance	8,935		8,935		20,138
Related Allowance
Average Recorded Balance	7,204	19,406	9,246	10,278
Recorded Investment	19,142		19,142		19,161
Unpaid Principal Balance	23,652		23,652		19,823
Related Allowance	2,525		2,525		3,747
Average Recorded Balance	19,502	24,612	19,376	24,941
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	156		156		386
Unpaid Principal Balance	156		156		386
Related Allowance
Average Recorded Balance	164	406	269	432
Recorded Investment	184		184		319
Unpaid Principal Balance	184		184		794
Related Allowance	69		69		148
Average Recorded Balance	159	751	216	681
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment	1,080		1,080		1,069
Unpaid Principal Balance	1,987		1,987		1,897
Related Allowance
Average Recorded Balance	966	1,321	1,052	1,399
Recorded Investment	99		99		72
Unpaid Principal Balance	136		136		72
Related Allowance	2		2		37
Average Recorded Balance	85	1,321	79	1,399
Home Equity Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Balance
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Balance
Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Balance
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Balance
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Balance
Recorded Investment
Unpaid Principal Balance
Related Allowance
Average Recorded Balance