Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share
Antidilutive common share equivalents excluded from computation of earnings per share amount (in shares)	0	0	0	0
Net Income (Numerator)
Basic earnings per share (in dollars)	$ 151,048	$ 398,375	$ 549,678	$ 988,375
Diluted earnings per share (in dollars)	$ 151,048	$ 398,375	$ 549,678	$ 988,375
Weighted Average Shares (Denominator)
Basic earnings per share (in shares)	217,873,000	234,208,000	221,145,000	235,483,000
Dilutive common share equivalents (in shares)	1,236,000	1,441,000	1,052,000	1,289,000
Diluted earnings per share (in shares)	219,109,000	235,649,000	222,197,000	236,772,000
Per Share Amount
Basic (in dollars per share)	$ 0.69	$ 1.70	$ 2.49	$ 4.20
Diluted (in dollars per share)	$ 0.69	$ 1.69	$ 2.47	$ 4.17