Quarterly report pursuant to Section 13 or 15(d)

Stockholders' equity (Details)

v3.7.0.1
Stockholders' equity (Details)
$ / shares in Units, $ in Millions
 1 Months Ended
Feb. 29, 2016
shares
Feb. 09, 2016
USD ($)
shares
Jun. 30, 2017
$ / shares
shares
Dec. 31, 2016
$ / shares
shares
Jan. 19, 2016
$ / shares
shares
Equity [Abstract]          
Common stock, shares authorized (in shares)     75,000,000 75,000,000  
Common stock, par value per share (in dollars per share) | $ / shares     $ 0.0001 $ 0.0001  
Preferred stock, shares authorized (in shares)     10,000,000 10,000,000  
Preferred stock, par value per share (in dollars per share) | $ / shares     $ 0.0001 $ 0.0001  
Common stock, shares outstanding (in shares)     25,228,278 25,050,628  
Preferred stock, shares outstanding (in shares)     0 0  
Class of Stock [Line Items]          
Maximum number of shares available for purchase for rights offering (in shares)         1,454,545
Rights conversion ratio into shares for rights offering         1
Exercise price (in dollars per share) | $ / shares         $ 2.75
Rights conversion ratio from common stock owned for rights offering         0.0582
Gross proceeds from issuance of stock from rights offering | $   $ 4.0      
Number of shares issued in rights offering (in shares)   1,454,545      
Number of shares issued for basic subscription rights from rights offering (in shares)   632,582      
Net proceeds form issuance of stock from rights offering | $   $ 3.9      
Initial Stockholders          
Class of Stock [Line Items]          
Shares of stock forfeited (in shares) 1,437,500