Computation of Earnings Per Share - Calculations Of Basic And Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income used for calculating basic and diluted earnings per common share	$ 122,456	$ 3,279	$ 193,582
Denominator:
Weighted average common shares used in the calculation of basic earnings per share	90,827	88,466	82,571
Common share equivalents associated with stock-based compensation plans	1,295	1,324	1,249
Shares used in the calculation of diluted earnings per share	92,122	89,790	83,820
Earnings per share:
Basic (in dollars per share)	$ 1.35	$ 0.04	$ 2.34
Diluted (in dollars per share)	$ 1.33	$ 0.04	$ 2.31