Share Repurchases (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	May 25, 2017
Text Block [Abstract]
Number of shares authorized for repurchase under the share repurchase program			$ 200,000,000
Shares repurchased	0.3	1.8
Value of shares repurchased	$ 25,000,000	$ 125,000,000
Treasury stock acquired, average cost per share (in usd per share)	$ 72.62	$ 70.13