Commitments and Contingencies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies
Additional period for which the entity may elect to extend the term of the lease	5 years
Additional tenant improvement allowance	$ 2,100
Tenant improvement allowance utilized and included in fixed assets and deferred rent	0	$ 200
Amount available for tenant improvements	500
Rent expense	2,700	$ 2,600	$ 2,300
Future minimum lease payments under non-cancelable operating leases
2017	1,321
2018	1,314
2019	1,341
Thereafter	454
Total	$ 4,430