Summary of significant accounting policies - Narrative (Details)		1 Months Ended	10 Months Ended	12 Months Ended
	Feb. 03, 2015 USD ($) $ / shares shares	Jan. 31, 2015	Dec. 31, 2014 USD ($) shares	Dec. 31, 2015 USD ($) segment shares
Entity Location [Line Items]
Number of operating segments | segment				1
IPO proceeds, net of issuance costs | $	$ 79,900,000		$ 0	$ 80,435,430
Common stock, number of shares issued from conversion of preferred stock (in shares)	6,971,108
Common stock, shares authorized (shares)			61,000,000	100,000,000
IPO issuance costs | $	$ 1,848,737
Reverse stock split conversion ratio		0.2335
IPO underwriting discounts and commissions | $	$ 6,150,134
IPO
Entity Location [Line Items]
Common stock, shares issued	5,491,191
Common stock, price per share (in usd per share) | $ / shares	$ 16.00
Over-Allotment Option
Entity Location [Line Items]
Common stock, shares issued	91,191
United States
Entity Location [Line Items]
Number of geographic segments | segment				1