Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic
Net income	$ 6,092	$ 6,060	$ 17,962	$ 17,518
Weighted-average common shares outstanding (in shares)	10,345,497	10,299,213	10,337,401	10,296,131
Basic earnings per share (in dollars per share)	$ 0.59	$ 0.59	$ 1.74	$ 1.70
Diluted
Net income	$ 6,092	$ 6,060	$ 17,962	$ 17,518
Weighted-average common shares outstanding (in shares)	10,345,497	10,299,213	10,337,401	10,296,131
Effect of dilutive restricted stock, stock options and stock appreciation rights (in shares)	161,363	126,585	162,680	136,090
Weighted-average common shares outstanding assuming dilution (in shares)	10,506,860	10,425,798	10,500,081	10,432,221
Diluted earnings per share (in dollars per share)	$ 0.58	$ 0.58	$ 1.71	$ 1.68