Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net Income Per Common Share
Number of outstanding options not included in computation of Diluted EPS (in shares)	0	0	2,000	673,000
Numerator
Net income	$ 41,322	$ 36,268	$ 108,659	$ 77,363
Denominator
Weighted average number of common shares outstanding	51,627,000	50,616,000	51,421,000	51,143,000
Effect of outstanding share-based awards	844,000	666,000	803,000	739,000
Weighted average number of shares for diluted net income per common share	52,471,000	51,282,000	52,224,000	51,882,000
Basic earnings per share (in dollars per share)	$ 0.80	$ 0.72	$ 2.11	$ 1.51
Diluted earnings per share (in dollars per share)	$ 0.79	$ 0.71	$ 2.08	$ 1.49