Computation of Earnings Per Share - Calculations Of Basic And Diluted (Loss) Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income used for calculating basic and diluted income per common share	$ 41,388	$ 11,753	$ 165,589	$ 38,436
Denominator:
Weighted average number of common shares used in the calculation of basic (loss) income per share (in shares)	89,846	90,854	89,947	90,969
Common stock equivalents associated with stock-based compensation plans (in shares)	1,041	1,294	1,142	1,275
Shares used in the calculation of diluted income per share (in shares)	90,887	92,148	91,089	92,244
Basic income per share (in dollars per share)	$ 0.46	$ 0.13	$ 1.84	$ 0.42
Diluted income per share (in dollars per share)	$ 0.46	$ 0.13	$ 1.82	$ 0.42