Reduction in force (Details)	1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended
	Oct. 31, 2015 USD ($) employee	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Reduction in force
Reduction of workforce (as a percent)	50.00%
Number of full time employees | employee	20
Severance and related costs	$ 1,100,000
Severance paid		$ 114,000	$ 78,000	$ 635,000	$ 349,000
Severance and related costs payable			$ 0