Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan Assets
Expected contributions to the defined benefit pension plan in 2018	$ 2.8
Net actuarial loss	58.7	$ 61.1
Expense provision for 401 (k) plans	4.2	4.0	$ 4.0
Hedge Funds Investments [Member]
Pension Plan Assets
Investments in hedge funds which do not have readily determinable fair values	30.7	39.1
Employee Pension Plans [Member]
Pension Plan Assets
Other comprehensive gain (loss)	2.4	$ 4.3	$ 0.7
Amount to be amortized from other comprehensive loss into cost in 2018	$ 2.1
Discount rate (as a percent)	3.50%	3.90%
Expected return on assets (as a percent)	6.00%	6.00%	6.50%
Other Multiemployer Pension Plans
Pension Plan Assets
Multiemployer Plan, Period Contributions	$ 32.1	$ 52.5	$ 55.8