Common Stock (Details) (USD $)	0 Months Ended	1 Months Ended	12 Months Ended
	Feb. 21, 2013	Sep. 30, 2002	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Common Stock [Abstract]
Aggregate quarterly cash dividends			$ 3,676,000	$ 3,264,000	$ 2,828,000
Cash dividends paid, per share			$ 0.56	$ 0.50	$ 0.44
Date dividends declared			Feb. 21, 2013
Cash dividends declared	$ 0.15
Date dividends will be paid			Mar. 22, 2013
Date dividends will be recorded			Mar. 14, 2013
Percentage of common stock authorized for repurchase		5.00%
Cumulative number of shares of treasury stock repurchased under program		688,442
Average price of common shares repurchased		$ 20.65
Total cost of common shares repurchased		$ 14,200,000
Remaining shares available under stock repurchase program		227,242