401(k) Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Contribution Plan [Abstract]
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	70.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match, Maximum per Employee	6.00%
Total expense related to 401(k) plan	$ 0.9	$ 1.4	$ 4.2