Segments and Geographic Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of operating segments | segment									1
Number of reportable segments | segment									1
Revenues	$ 43,770	$ 43,636	$ 42,325	$ 41,444	$ 44,184	$ 45,355	$ 44,635	$ 45,388	$ 171,175	$ 179,561	$ 189,628
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									166,790	173,852	185,741
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 4,385	$ 5,709	$ 3,887