Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Income Per Common Share
Number of outstanding options not included in computation of Diluted EPS (in shares)	0	459,000	6,000	2,019,000
Numerator
Net income	$ 40,244	$ 31,475	$ 67,336	$ 41,095
Denominator
Weighted average number of common shares outstanding	51,418,000	51,357,000	51,318,000	51,407,000
Effect of outstanding share-based awards	776,000	614,000	786,000	775,000
Weighted average number of shares for diluted net income per common share	52,194,000	51,971,000	52,104,000	52,182,000
Basic earnings per share (in dollars per share)	$ 0.78	$ 0.61	$ 1.31	$ 0.80
Diluted earnings per share (in dollars per share)	$ 0.77	$ 0.61	$ 1.29	$ 0.79