Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share
Antidilutive common share equivalents excluded from computation of earnings per share amount (in shares)	0	0
Net Income (Numerator)
Basic earnings per share - net income (in dollars)	$ 200,817	$ 62,737
Diluted earnings per share - net income (in dollars)	$ 200,817	$ 62,737
Weighted average common shares outstanding (in shares)
Weighted average common shares outstanding - basic (in shares)	242,943	243,202
Dilutive common share equivalents (in shares)	1,603	1,406
Weighted average common shares outstanding - diluted (in shares)	244,546	244,608
Per Share Amount
Basic (in dollars per share)	$ 0.83	$ 0.26
Diluted (in dollars per share)	$ 0.82	$ 0.26