Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Obligations for base rent and CAM costs under facility and other non-cancelable operating leases
2018	$ 4,591
2019	4,472
2020	2,498
Total minimum lease payments	11,561
Total rent and CAM expense	$ 4,100	$ 4,800	$ 2,900