Commitments and Contingencies (Details) - October 2015 Share Repurchase Program - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	2 Months Ended	9 Months Ended	12 Months Ended	23 Months Ended
	Oct. 27, 2017	Dec. 31, 2015	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2017	Oct. 26, 2015
Stock Repurchases
Amount authorized under stock repurchase plan						$ 200.0
Share repurchases made in open market (in shares)	20,994	345,044	204,881	1,828,183	2,378,108
Average Price Paid per Share (in dollars per share)		$ 53.46	$ 75.42	$ 58.40
Aggregate Cost	$ 1.8	$ 18.4	$ 15.5	$ 106.8	$ 140.7