Commitments and Contingencies Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Oct. 04, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Estimated withdrawal liability	$ 2.4	$ 3.3		$ 3.1	$ 13.5
Remaining estimated withdrawal liability	$ 7.9			$ 7.9
Withdrawal from multi-employer pension plan
Restructuring Cost and Reserve [Line Items]
Estimated withdrawal liability			$ 12.5
Remaining estimated withdrawal liability							$ 23.0
Arbitration proceeding - withdrawal from multi-employer pension plan | Subsequent Event
Restructuring Cost and Reserve [Line Items]
Estimate of possible loss						$ 23.3