Commitments and contingencies (Details)		6 Months Ended
	Dec. 10, 2015 USD ($) shares	Jun. 30, 2016 USD ($) d shares	Jun. 30, 2015 USD ($)	May 25, 2016 shares	May 18, 2016 shares	Feb. 26, 2016 Motion	Jan. 05, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Jun. 13, 2014 Lawsuit
Loss Contingencies [Line Items]
Amount of milestone payment payable		$ 7,500,000
Potential future milestone payments on each additional final marketing approval		$ 1,000,000
Number of purported securities class action lawsuits pending | Lawsuit									3
Number of day's court afforded the plaintiffs to amend their complaint | d		30
Litigation settlement payment	$ 4,000,000	$ 700,000	$ 0
Litigation settlement due in shares		$ 700,000						$ 4,500,000
Common stock issued (in shares) | shares		68,371,643						66,480,065
Common stock issued for litigation settlement (in shares) | shares				1,561,578	1,561,578
Number of motions filed by the company | Motion						2
Minimum [Member]
Loss Contingencies [Line Items]
Legal fees to be reimbursed by insurance carrier	$ 3,500,000
Common stock issued (in shares) | shares	1,200,000
Maximum [Member]
Loss Contingencies [Line Items]
Common stock issued (in shares) | shares	1,800,000
Litigation settlement due in shares of common [Member]
Loss Contingencies [Line Items]
Litigation settlement due in shares	$ 4,500,000
Corporation Stockholder Derivative Litigation [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Common stock issued (in shares) | shares							186,666
Corporation Stockholder Derivative Litigation [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Common stock issued (in shares) | shares							280,000
Corporation Stockholder Derivative Litigation [Member] | Litigation settlement due in shares of common [Member]
Loss Contingencies [Line Items]
Litigation settlement due in shares							$ 700,000