Stockholders' Equity and Earnings Per Share (Earnings Per Share Calculation) (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
Basic:
Net income	$ 224,742	$ 99,352	$ 429,736	$ 244,176
Basic weighted-average number of shares outstanding (in shares)	141,868	141,486	141,758	143,150
Basic EPS (in dollars per share)	$ 1.58	$ 0.70	$ 3.03	$ 1.71
Diluted:
Net income	$ 224,742	$ 99,352	$ 429,736	$ 244,176
Basic weighted-average number of shares outstanding (in shares)	141,868	141,486	141,758	143,150
Diluted potential common shares (in shares)	1,172	341	1,205	410
Diluted weighted-average number of shares outstanding (in shares)	143,040	141,827	142,963	143,560
Diluted EPS (in dollars per share)	$ 1.57	$ 0.70	$ 3.01	$ 1.70