Subsequent events (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended			3 Months Ended
		Jul. 24, 2019	Jun. 30, 2019	May 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Sep. 30, 2019
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Total remaining lease payments						$ 890
Stock Options [Member]
Number of Stock Options [Abstract]
Options, exercised (in shares)						(71,250)
Expiration Date, April 2019 [Member]
Warrants and Rights [Abstract]
Expiration date	[1]					Apr. 30, 2019
Exercise price (in dollars per share)	[1]					$ 3.75
Expiration Date, July 2019 [Member]
Warrants and Rights [Abstract]
Expiration date						Jul. 24, 2019
Expiration Date, July 2019 [Member] | Minimum [Member]
Warrants and Rights [Abstract]
Exercise price (in dollars per share)						$ 3.75
Expiration Date, July 2019 [Member] | Maximum [Member]
Warrants and Rights [Abstract]
Exercise price (in dollars per share)						$ 12.25
Subsequent Event [Member]
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Total remaining lease payments							$ 1,107
Subsequent Event [Member] | Stock Options [Member]
Number of Stock Options [Abstract]
Options, exercised (in shares)				(15,000)
Options, Exercise price (in dollars per share)				$ 1.29
Common stock shares issued on exercise of options (in shares)				7,586
Subsequent Event [Member] | Expiration Date, April 2019 [Member]
Warrants and Rights [Abstract]
Expiration date					Apr. 30, 2019
Warrants expired (in shares)					(137,143)
Exercise price (in dollars per share)					$ 3.75
Subsequent Event [Member] | Expiration Date, July 2019 [Member]
Warrants and Rights [Abstract]
Expiration date		Jul. 24, 2019
Warrants expired (in shares)		(1,239,769)
Subsequent Event [Member] | Expiration Date, July 2019 [Member] | Minimum [Member]
Warrants and Rights [Abstract]
Exercise price (in dollars per share)		$ 3.75
Subsequent Event [Member] | Expiration Date, July 2019 [Member] | Maximum [Member]
Warrants and Rights [Abstract]
Exercise price (in dollars per share)		$ 12.25
Subsequent Event [Member] | Series C Convertible Preferred Stock [Member]
Subsequent Events [Abstract]
Number of common shares issued on conversion of preferred stock (in shares)			1,775,093

[1] These warrants are classified as liabilities.