Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Employee contribution limit per calendar year to 401 (k) Plan (as a percent of compensation)	60.00%
Employer match of employee contributions of first 6% of eligible compensation (as a percent)	50.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 2.3	$ 2.0	$ 2.1