Reconciliation of Generally Accepted Accounting Principles Capital to Regulatory Tier One and Total Capital (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Stockholders' Equity to Regulatory Capital [Line Items]
Consolidated GAAP capital	$ 189,187	$ 218,988	$ 221,245	$ 247,299
Unrealized gains on certain available-for-sale securities, net of tax	(13,253)	(10,321)
Unrealized losses on defined benefit pension plan	2,558	2,605
Disallowed deferred tax asset	(291)	(2,673)
Tier 1 capital	178,201	208,599
Unrealized gains on certain available-for-sale equity securities	89
Allowance for loan losses	7,794	7,764	6,934	7,645
Total regulatory capital	$ 186,084	$ 216,363