Net Income per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Income per Share
Net income	$ 4,850	$ 6,370	$ 15,766	$ 20,884
Basic weighted average shares outstanding	16,068	15,628	15,930	15,603
Basic net income per common share (in dollars per share)	$ 0.30	$ 0.41	$ 0.99	$ 1.34
Diluted Shares Outstanding
Basic weighted average shares outstanding	16,068	15,628	15,930	15,603
Weighted average stock options outstanding (in shares)	422	343	397	314
Diluted weighted average shares outstanding	16,490	15,971	16,327	15,917
Diluted net income per common share (in dollars per share)	$ 0.29	$ 0.40	$ 0.97	$ 1.31
Potentially dilutive shares excluded from diluted per share amounts:
Stock options (in shares)	140	96	140	96
Potentially anti-dilutive shares excluded from diluted per share amounts:
Stock options (in shares)	20	167	45	249