Employee Retirement Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Retirement Benefits [Abstract]
Actual employer contributions to defined benefit plans	$ 0.8	$ 1.6	$ 1.7	$ 4.7
Expected full year contributions by the employer to defined benefit plans	2.5		2.5
Contributions to multiemployer plan	$ 0.5	$ 0.6	1.4	$ 1.7
Expected full year contributions by the employer to the multiemployer plan			$ 1.9