Stock-based compensation, Unvested Stock Option Activity (Details) - Stock Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options [Roll Forward]
Unvested balance at beginning of period (in shares)	3,003,512	3,394,468
Granted (in shares)	400,000	875,000
Vested (in shares)	(1,553,125)	(1,265,956)
Forfeited/expired (in shares)	0	0
Unvested balance at end of period (in shares)	1,850,387	3,003,512
Weighted Average Grant Date Fair Value [Abstract]
Unvested balance at beginning of period (in dollars per share)	$ 1.05	$ 0.82
Granted (in dollars per share)	1.11	1.56
Vested (in dollars per share)	0.96	0.78
Forfeited/expired (in dollars per share)	0	0
Unvested balance at end of period (in dollars per share)	$ 1.15	$ 1.05