Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 218,653	$ 214,726
Weighted-average common shares outstanding (in shares)	212,610,000	214,870,000
Dilutive effect of stock-based awards and stock options (in shares)	992,000	943,000
Diluted weighted-average shares outstanding (in shares)	213,602,000	215,813,000
Basic earnings per share (in dollars per share)	$ 1.03	$ 1.00
Diluted earnings per share (in dollars per share)	$ 1.02	$ 0.99
Antidilutive securities (in shares)	0	0