Stockholders' Equity and Earnings Per Share (Earnings Per Share Calculation) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic:
Net income	$ 204,994	$ 144,824
Basic weighted-average number of shares outstanding (in shares)	141,646	144,814
Basic EPS (in dollars per share)	$ 1.45	$ 1.00
Diluted:
Net income	$ 204,994	$ 144,824
Basic weighted-average number of shares outstanding (in shares)	141,646	144,814
Diluted potential common shares (in shares)	1,198	471
Diluted weighted-average number of shares outstanding (in shares)	142,844	145,285
Diluted EPS (in dollars per share)	$ 1.44	$ 1.00