Troubled Debt Restructured Loans for Specific Segments of the Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Modifications [Line Items]
Restructured accruing	$ 3,614	$ 5,286
Restructured non-accruing	1,304	4,976
Balance	4,918	10,262
Specific allowance	1,223	1,883
Restructured and subsequently defaulted	0	509
Commercial Loan
Financing Receivable, Modifications [Line Items]
Restructured accruing	2,600	1,696
Restructured non-accruing	0	469
Balance	2,600	2,165
Specific allowance	552	254
Restructured and subsequently defaulted	0	0
Commercial Investor Real Estate
Financing Receivable, Modifications [Line Items]
Restructured accruing	0	0
Restructured non-accruing	0	1,269
Balance	0	1,269
Specific allowance	0	93
Restructured and subsequently defaulted	0	0
Commercial Owner Occupied Real Estate
Financing Receivable, Modifications [Line Items]
Restructured accruing	1,014	0
Restructured non-accruing	0	2,475
Balance	1,014	2,475
Specific allowance	204	509
Restructured and subsequently defaulted	0	0
All Other
Financing Receivable, Modifications [Line Items]
Restructured accruing	0	3,590
Restructured non-accruing	1,304	763
Balance	1,304	4,353
Specific allowance	467	1,027
Restructured and subsequently defaulted	0	509
Commercial Acquisition, Development and Construction
Financing Receivable, Modifications [Line Items]
Restructured accruing	0	0
Restructured non-accruing	0	0
Balance	0	0
Specific allowance	0	0
Restructured and subsequently defaulted	$ 0	$ 0