Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 53,765	$ 56,656	$ 53,617	$ 46,901	$ 49,299	$ 53,889	$ 51,984	$ 61,902	$ 210,939	$ 217,074	$ 190,355
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									186,847	193,054	164,952
Americas, excluding U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									3,028	2,562	4,552
Europe, Middle East, India, Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									13,998	14,256	15,437
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 7,066	$ 7,202	$ 5,414