Capital Stock and Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 1,298	$ 423,635	$ 531,451
Denominator:
Basic weighted-average shares outstanding (in shares)	153,186	157,054	165,672
Effect of dilutive securities – employee stock compensation plan (in shares)	722	750	832
Diluted weighted-average shares outstanding (in shares)	153,908	157,804	166,504
Basic (in dollars per share)	$ 0.01	$ 2.70	$ 3.21
Diluted (in dollars per share)	$ 0.01	$ 2.68	$ 3.19