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, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income used for calculating basic and diluted income per common share	$ 266,745	$ 233,290	$ 122,456
Denominator:
Weighted average common shares used in the calculation of basic income per share (in shares)	89,315	89,817	90,827
Common stock equivalents associated with stock-based compensation plans (in shares)	702	1,154	1,295
Shares used in the calculation of diluted income per share (in shares)	90,017	90,971	92,122
Income per share:
Basic (in dollars per share)	$ 2.99	$ 2.60	$ 1.35
Diluted (in dollars per share)	2.96	2.56	$ 1.33
Sale of intellectual property, income tax benefit (in dollars per share)	$ 0.31	$ 420,000