Summary of Significant Accounting Policies (Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounting Policies [Abstract]
Net income	$ 101,066	$ 126,540	$ 210,308	$ 240,521
Shares used to compute basic earnings per common share (in shares)	147,478	151,863	148,473	152,587
Dilutive effect of stock options (in shares)	2,120	3,302	2,510	3,266
Shares used to compute diluted earnings per common share (in shares)	149,598	155,165	150,983	155,853
Basic earnings per common share (in USD per share)	$ 0.69	$ 0.83	$ 1.42	$ 1.58
Diluted earnings per common share (in USD per share)	$ 0.68	$ 0.82	$ 1.39	$ 1.54