Retirement Savings Plan (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Postemployment Benefits [Abstract]
Percentage of maximum limit for employees to contribute their cash compensation			75.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay			4.00%
Total plan expenses	$ 0.8	$ 1.8	$ 1.7	$ 3.9