Stockholders' Equity and Earnings Per Share (Earnings Per Share Calculation) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic:
Net income	$ 225,449	$ 159,537	$ 655,185	$ 403,713
Basic weighted-average number of shares outstanding (in shares)	141,880	141,498	141,799	142,595
Basic EPS (in dollars per share)	$ 1.59	$ 1.13	$ 4.62	$ 2.83
Diluted:
Net income	$ 225,449	$ 159,537	$ 655,185	$ 403,713
Basic weighted-average number of shares outstanding (in shares)	141,880	141,498	141,799	142,595
Diluted potential common shares (in shares)	1,263	545	1,252	487
Diluted weighted-average number of shares outstanding (in shares)	143,143	142,043	143,051	143,082
Diluted EPS (in dollars per share)	$ 1.57	$ 1.12	$ 4.58	$ 2.82