Common Stock, warrants, stock-based compensation, stock options, restricted stock and restricted stock units - Warrants (Details) - Outstanding warrants	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Number outstanding
Outstanding at the beginning of the period (in shares)	86,090
Issued (in shares)	10,000
Exercised (in shares)	(16,718)
Cancelled (in shares)	(3,331)
Outstanding at the end of the period (in shares)	76,041
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares	$ 9.14
Issued (in dollars per share) | $ / shares	4.83
Exercised (in dollars per share) | $ / shares	11.73
Cancelled (in dollars per share) | $ / shares	11.73
Outstanding at the end of the period (in dollars per share) | $ / shares	$ 10.10
Obligation to issue warrants, in shares	93,341