Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 466,295	$ 369,526	$ 684,948	$ 584,252
Weighted-average common shares outstanding (in shares)	211,673,000	215,085,000	212,139,000	214,978,000
Dilutive effect of stock-based awards and stock options (in shares)	836,000	977,000	940,000	966,000
Diluted weighted-average shares outstanding (in shares)	212,509,000	216,062,000	213,079,000	215,944,000
Basic earnings per share (in dollars per share)	$ 2.20	$ 1.72	$ 3.23	$ 2.72
Diluted earnings per share (in dollars per share)	$ 2.19	$ 1.71	$ 3.21	$ 2.71
Antidilutive securities (in shares)	0	0	0	0