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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accounting Policies [Abstract]
Net income	$ 133,778	$ 101,066	$ 263,248	$ 210,308
Shares used to compute basic earnings per common share (in shares)	142,074	147,478	142,638	148,473
Dilutive effect of stock options (in shares)	2,138	2,120	2,121	2,510
Shares used to compute diluted earnings per common share (in shares)	144,212	149,598	144,759	150,983
Basic earnings per common share (in USD per share)	$ 0.94	$ 0.69	$ 1.85	$ 1.42
Diluted earnings per common share (in USD per share)	$ 0.93	$ 0.68	$ 1.82	$ 1.39