Nature of business and basis of presentation - IPO (Details) $ / shares in Units, $ in Thousands				6 Months Ended
	Jul. 25, 2016 USD ($) $ / shares	Jun. 21, 2016 USD ($) $ / shares shares	Jun. 07, 2016	Jun. 30, 2016 USD ($)	Jun. 27, 2016 shares
Subsidiary, Sale of Stock [Line Items]
Net proceeds				$ 65,100
Number of shares of common stock issued for convertible preferred stock | shares					10,126,118
IPO
Subsidiary, Sale of Stock [Line Items]
Reverse stock split ratio			0.2564
Common stock issued and sold | shares		5,000,000
Share price | $ / shares		$ 14.00
Net proceeds	$ 64,500	$ 60,800
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Share price | $ / shares	$ 14.00
Net proceeds	$ 3,700