Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic EPS [Abstract]
Weighted average common shares outstanding (in shares)	44,007,000	43,865,000	44,079,000	43,829,000
Net income	$ 19,281	$ 27,640	$ 37,447	$ 45,649
Basic EPS (in dollars per share)	$ 0.44	$ 0.63	$ 0.85	$ 1.04
Diluted EPS [Abstract]
Weighted average common shares outstanding (in shares)	44,007,000	43,865,000	44,079,000	43,829,000
Dilutive effect of common stock options and restricted stock (in shares)	523,000	498,000	510,000	500,000
Weighted average common shares and common share equivalents (in shares)	44,530,000	44,363,000	44,589,000	44,329,000
Net income	$ 19,281	$ 27,640	$ 37,447	$ 45,649
Diluted EPS (in dollars per share)	$ 0.43	$ 0.62	$ 0.84	$ 1.03
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options excluded from calculation of diluted EPS (in shares)	339,109	503,058	340,034	500,541