Segment Reporting and Significant Customer Information - Revenue for Individual Countries that Exceed 10% of Total Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Revenue, Major Customer [Line Items]
Revenues	$ 26,898	$ 25,505	$ 28,184	$ 30,825	$ 27,062	$ 25,301	$ 28,075	$ 30,884	$ 111,412	$ 111,322
United States
Revenue, Major Customer [Line Items]
Revenues									61,375	61,257
United Kingdom
Revenue, Major Customer [Line Items]
Revenues									19,961	21,034
Germany
Revenue, Major Customer [Line Items]
Revenues									12,176	12,257
Rest of the world
Revenue, Major Customer [Line Items]
Revenues									$ 17,900	$ 16,774