New Accounting Standards (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Diluted weighted average shares outstanding		121,910,763	126,140,309	122,686,552	127,403,089
Excess tax benefit from stock option exercises, financing activities	[1]			$ 0	$ 15,679
New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefits		$ 7,000		$ 14,000
Diluted weighted average shares outstanding		121,900,000		122,700,000
Increase in earnings per share as a result of the adoption (in dollars per share)		$ 0.05		$ 0.09
Previous Accounting Guidance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefits			$ 5,000		16,000
Diluted weighted average shares outstanding		121,100,000		121,900,000
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit from stock option exercises, operating activities				$ 14,000
Excess tax benefit from stock option exercises, financing activities					$ 16,000

[1] Due to the prospective adoption of ASU 2016-09, the excess tax benefits from stock option exercises of $14 million at September 30, 2016 were presented as a component of operating activities in the same manner as other cash flows related to income taxes. The 2015 balance of $16 million, under the previous guidance, remains in the financing activities section. See further discussion at Note 2—New Accounting Standards.