Retirement Savings Plan (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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	$ 1.2	$ 2.1