Organization and operations (Details)		1 Months Ended	9 Months Ended	10 Months Ended	12 Months Ended
	Feb. 03, 2015 USD ($) $ / shares shares	Feb. 28, 2015 USD ($) $ / shares shares	Sep. 30, 2016 segment	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)
Subsidiary, Sale of Stock [Line Items]
Number of reportable segments | segment			2		2
Proceeds from initial public offering, net of offering costs	$ 79,900,000	$ 79,900,000		$ 0	$ 0	$ 80,435,430
Payments of stock issuance costs		$ 8,000,000
Accumulated deficit					76,645,613	$ 37,152,490
Cash, cash equivalents, and marketable securities					$ 61,074,973
IPO
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued | shares	5,491,191	5,491,191
Common stock, price per share (in usd per share) | $ / shares	$ 16.00	$ 16.00
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued | shares	91,191	91,191