Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
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)	$ 75,496	$ 194,302	$ 262,836	$ 398,630
Diluted earnings per share (in dollars)	$ 75,496	$ 194,302	$ 262,836	$ 398,630
Weighted Average Shares (Denominator)
Basic earnings per share (in shares)	210,343,000	221,505,000	211,798,000	222,781,000
Dilutive common share equivalents (in shares)	1,035,000	1,014,000	903,000	960,000
Diluted earnings per share (in shares)	211,378,000	222,519,000	212,701,000	223,741,000
Per Share Amount
Basic (in dollars per share)	$ 0.36	$ 0.88	$ 1.24	$ 1.79
Diluted (in dollars per share)	$ 0.36	$ 0.87	$ 1.24	$ 1.78