Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statement of Stockholders' Equity [Abstract]
Cash dividends declared, per share	$ 0.74	$ 0.72	$ 0.70
Tax of unrealized gain on securities available for sale	$ 71	$ 551	$ 530
Tax of reclassification adjustment for net security gain, included in net income	13	8	205
Tax of amortization of unrealized gain on securities available for sale transferred to securities held to maturity included in net income	168	60
Tax of unrealized loss on interest rate swap	287	31
Tax of reclassification of interest rate swap settlements included in earnings	$ 72	$ 21