Annual report pursuant to Section 13 and 15(d)

Stockholders' equity (Details)

v3.8.0.1
Stockholders' equity (Details)
12 Months Ended
Dec. 31, 2017
item
$ / shares
shares
Dec. 31, 2016
$ / shares
shares
Stockholders' equity    
Temporary Equity, Shares Issued 0 0
Temporary Equity, Shares Outstanding 0 0
Common Stock    
Number of votes per share | item 1  
Common Stock, Par or Stated Value Per Share | $ / shares $ 0.01 $ 0.01
Common Stock, Shares Authorized 200,000,000 200,000,000
Common Stock, Shares, Issued 22,590,897 22,501,640
Common Stock, Shares, Outstanding 22,590,897 22,501,640
Series A Redeemable Preferred Stock    
Stockholders' equity    
Shares authorized 5,000,000  
Par value (in dollars per share) | $ / shares $ 0.01