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, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income used for calculating basic and diluted income per share	$ 148,865	$ 271,236	$ 164,100	$ 16,964	$ 55,077	$ 75,097	$ 584,201	$ 147,138
Denominator:
Weighted average number of common shares used in the calculation of basic income per share (in shares)	83,566			89,378			85,877	89,307
Dilutive effect of outstanding awards associated with stock-based compensation plans (in shares)	1,200			577			1,048	695
Shares used in the calculation of diluted income per share (in shares)	84,766			89,955			86,925	90,002
Basic income per share (in dollars per share)	$ 1.78			$ 0.19			$ 6.80	$ 1.65
Diluted income per share (in dollars per share)	$ 1.76			$ 0.19			$ 6.72	$ 1.63