Troubled Debt Restructured Loans for Specific Segments of the Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Restructured accruing	$ 2,792	$ 5,286
Restructured non-accruing		4,976
Balance	2,792	10,262
Specific allowance	530	1,883
Restructured and subsequently defaulted		509
Commercial Loan
Financing Receivable, Modifications [Line Items]
Restructured accruing	1,771	1,696
Restructured non-accruing		469
Balance	1,771	2,165
Specific allowance	319	254
Commercial Investor Real Estate
Financing Receivable, Modifications [Line Items]
Restructured non-accruing		1,269
Balance		1,269
Specific allowance		93
Commercial Owner Occupied Real Estate
Financing Receivable, Modifications [Line Items]
Restructured accruing	1,021
Restructured non-accruing		2,475
Balance	1,021	2,475
Specific allowance	211	509
All Other
Financing Receivable, Modifications [Line Items]
Restructured accruing		3,590
Restructured non-accruing		763
Balance		4,353
Specific allowance		1,027
Restructured and subsequently defaulted		$ 509