401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Defined contribution plan, employer matching contribution, percent of match	50.00%
Defined contribution plan, employer matching contribution, percent	6.00%
Defined contribution plan, vesting period	5 years
Defined contribution plan, employer matching contribution, amount	$ 683	$ 671	$ 608