Stock-based compensation (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Oct. 27, 2016
Stock Options [Member]
Number of Stock Options [Roll Forward]
Outstanding at beginning period (in shares)	2,684,352	1,308,835
Granted (in shares)	2,340,000	1,487,500
Exercised (in shares)	0	0
Expired/cancelled (in shares)	(523,830)	(111,983)
Outstanding at end of period (in shares)	4,500,522	2,684,352
Exercisable at end of period (in shares)	2,200,672
Options expected to vest at end of period (in shares)	2,049,850
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 1.54	$ 2.76
Granted (in dollars per share)	0.58	1.15
Exercised (in dollars per share)	0	0
Expired/cancelled (in dollars per share)	2.07	10.70
Outstanding at end of period (in dollars per share)	1.02	$ 1.54
Exercisable at end of period (in dollars per share)	1.48
Options expected to vest at end of period (in dollars per share)	$ 0.59
Stock Incentive Plan 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance (in shares)	8,294,400		10,294,400