Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net Income (Numerator)
Basic earnings per share - net income (in dollars)	$ 227,551	$ 200,817
Diluted earnings per share - net income (in dollars)	$ 227,551	$ 200,817
Weighted average common shares outstanding (in shares)
Weighted average common shares outstanding - basic (in shares)	236,623	242,943
Dilutive common share equivalents (in shares)	1,100	1,603
Weighted average common shares outstanding - diluted (in shares)	237,723	244,546
Per Share Amount
Basic (in dollars per share)	$ 0.96	$ 0.83
Diluted (in dollars per share)	$ 0.96	$ 0.82