Restructuring - Narrative (Details) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 position	Mar. 31, 2019 position	Sep. 30, 2018 USD ($)	Jun. 30, 2019 position	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of positions eliminated | position		9	3		12
Restructuring	$ (19)			$ 1		$ 243	$ (46)
Cash and cash equivalents	634			7,054		634	7,054	$ 6,335	$ 10,761
Restricted cash held	342			$ 342		342	$ 342
Short-term debt	3,000					3,000
Credit line borrowings	1,323					1,323		$ 2,219
Proceeds from issuance of subordinated convertible promissory notes						1,700
Severance and Related Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring						200
Revolving Credit Facility
Restructuring Cost and Reserve [Line Items]
Credit line borrowings	$ 1,300					$ 1,300