Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum age to participate in 401(k) plan	18 years
Contribution expenses		$ 0.9	$ 1.0
Non-highly Compensated Employees
Portion of eligible compensation that may be deferred (as a percent)	75.00%
Highly Compensated Employees
Portion of eligible compensation that may be deferred (as a percent)	15.00%