Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Net income	$ 111,096	$ 132,168	$ 321,404	$ 372,689
Shares used to compute basic earnings per common share (in shares)	145,812	150,855	147,586	152,009
Dilutive effect of stock options (in shares)	2,095	3,372	2,372	3,302
Shares used to compute diluted earnings per common share (in shares)	147,907	154,227	149,958	155,311
Basic earnings per common share (in USD per share)	$ 0.76	$ 0.88	$ 2.18	$ 2.45
Diluted earnings per common share (in USD per share)	$ 0.75	$ 0.86	$ 2.14	$ 2.40