Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	6.00%
401(k) plan, expense recognized	$ 2.0	$ 2.2	$ 2.5
Contributory health and welfare plan, expense recognized	$ 3.4	$ 4.7	$ 6.0