Stock-based compensation, Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	May 29, 2018	Oct. 27, 2016
Stock Options [Member]
Number of Stock Options [Abstract]
Outstanding at beginning period (in shares)	4,908,038	4,342,765
Granted (in shares)	400,000	875,000
Exercised (in shares)	(15,000)	(86,250)
Expired/forfeited (in shares)	(150)	(223,477)
Outstanding at end of period (in shares)	5,292,888	4,908,038
Exercisable at end of period (in shares)	3,442,501
Options expected to vest at end of period (in shares)	1,850,387
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 1.90	$ 2.02
Granted (in dollars per share)	1.46	2.46
Exercised (in dollars per share)	1.29	1.74
Expired/forfeited (in dollars per share)	170.00	6.43
Outstanding at end of period (in dollars per share)	1.87	$ 1.90
Exercisable at end of period (in dollars per share)	1.87
Options expected to vest at end of period (in dollars per share)	$ 1.86
Stock Incentive Plan 2016 [Member]
Stock Options [Abstract]
Number of shares available for issuance (in shares)	41,774		3,134,365	2,058,880