Shareholders' Equity - Share Repurchase and Dividends (Details) - USD ($) $ / shares in Units, $ in Millions					1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 22, 2017	Jun. 23, 2017	Mar. 24, 2017	Feb. 22, 2016	Nov. 06, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Shareholders' Equity
Dividend declared (in dollars per share)				$ 0.04		$ 0.04	$ 0.04	$ 0.12	$ 0.12
Target dividend per annum (in dollars per share)								$ 0.16
Dividends paid, aggregate cost	$ 6.3	$ 6.4	$ 6.4					$ 19.1	$ 19.4
May 2017 Repurchase Program
Shareholders' Equity
Amount approved for repurchase of common stock						$ 225.0		$ 225.0
Common stock repurchased during the period (in shares)						3,063,133		4,658,063
Aggregate cost of common stock repurchased during the period						$ 87.9		$ 131.8
May 2017 Repurchase Program | Subsequent Event
Shareholders' Equity
Common stock repurchased during the period (in shares)					660,000
Aggregate cost of common stock repurchased during the period					$ 20.4