Stock-based compensation - Summary of Status of Company's Restricted Stock Option Activity (Details)	6 Months Ended
	Jun. 30, 2016 $ / shares shares
Shares
Beginning balance (in shares)	1,672,578
Granted (in shares)	1,250,000
Cancelled, expired, or forfeited (in shares)	(296,066)
Ending balance (in shares)	2,626,512
Exercisable at end of period (in shares)	749,205
Weighted Average Exercise Price
Granted (in dollars per share) | $ / shares	$ 2.75
Cancelled, expired, or forfeited (in dollars per share) | $ / shares	4.88
Ending balance (in dollars per share) | $ / shares	$ 4.06
Restricted Stock
Shares
Beginning balance (in shares)	0
Granted (in shares)	787,500
Cancelled, expired, or forfeited (in shares)	(26,250)
Ending balance (in shares)	761,250
Exercisable at end of period (in shares)	0
Weighted Average Exercise Price
Granted (in dollars per share) | $ / shares	$ 2.73
Cancelled, expired, or forfeited (in dollars per share) | $ / shares	2.73
Ending balance (in dollars per share) | $ / shares	$ 2.73