Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic earnings per share:
Net income	$ 9,063	$ 10,332	$ 24,122	$ 17,766
Weighted-average basic shares	14,920	13,818	14,484	13,613
Basic earnings per share (in dollars per share)	$ 0.61	$ 0.75	$ 1.67	$ 1.30
Diluted earnings per share:
Net income	$ 9,063	$ 10,332	$ 24,122	$ 17,766
Weighted-average basic shares	14,920	13,818	14,484	13,613
Effect of dilutive securities (in shares)	123	66	89	76
Weighted-average dilutive shares	15,043	13,884	14,573	13,689
Diluted earnings per share (in dollars per share)	$ 0.60	$ 0.74	$ 1.66	$ 1.28
Earnings Per Share
Antidilutive stock options excluded from the calculation of diluted earnings per share (in shares)	100,326	268,022	140,829	256,664
Exercise price of outstanding stock options, low end of range (in dollars per share)	$ 31.75	$ 26.01	$ 31.10	$ 26.01
Exercise price of outstanding stock options, high end of range (in dollars per share)	$ 40.99	$ 40.99	$ 40.99	$ 40.99