Income taxes - Provision for (benefit from) income taxes (Details) - USD ($)	3 Months Ended					12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
State						$ (20,000)	$ (18,000)
Foreign						(93,000)
Total current income tax provision						(113,000)	(18,000)
Deferred
Federal						(3,000)	(2,000)
State						(1,000)	(5,000)
Foreign						304,000
Total deferred income tax provision (benefit)						300,000	(7,000)
Total income tax provision (benefit)	$ 107,000	$ 125,000	$ (23,000)	$ (22,000)	$ (25,000)	$ 187,000	$ (25,000)	$ 0