Acquisition of Confluence - Supplemental pro forma financial information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Acquisition-related expenses
Business Acquisition [Line Items]
Net loss		$ 997		$ 1,351
Confluence
Business Acquisition [Line Items]
Revenue	$ 1,628	1,063	$ 6,422	3,366
Gross profit	435	298	3,081	1,102
Total operating expenses	33,885	18,736	99,457	48,122
Net loss	$ (32,740)	(17,875)	$ (94,187)	(45,627)
Confluence | Billed revenues
Business Acquisition [Line Items]
Net loss		$ (217)		$ (888)