XML 67 R54.htm IDEA: XBRL DOCUMENT v3.8.0.1
Common stock - Narrative (Details)
1 Months Ended 12 Months Ended
Apr. 30, 2014
shares
Mar. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
vote
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
shares
Class of Stock [Line Items]          
Common stock, shares authorized (shares)     100,000,000 100,000,000  
Common stock, par value (in usd per share) | $ / shares     $ 0.0001 $ 0.0001  
Common stock, number of votes per share | vote     1    
Restricted common stock, shares sold     0    
Stock issued under Employee Stock Purchase Plan     0    
Unvested restricted common stock          
Class of Stock [Line Items]          
Restricted common stock, shares sold 867,314 4,553,415      
Restricted common stock, price per share (in usd per share) | $ / shares   $ 0.0004      
Proceeds from sale of restricted common stock to founders | $   $ 1,950      
Restricted common stock, repurchase period     90 days    
Restricted common stock, repurchase price | $ / shares     $ 0.0004    
Restricted common stock, shares outstanding     5,251,075    
Restricted common stock, fair value of shares vested | $     $ 3,840,000 $ 9,646,000 $ 15,616,000
Issued, number of shares (shares)     0    
Unvested restricted common stock | Vests upon issuance          
Class of Stock [Line Items]          
Restricted common stock, percent vested     25.00%    
Unvested restricted common stock | Vests ratably over four years          
Class of Stock [Line Items]          
Restricted common stock, percent vested     75.00%    
Restricted common stock, vesting period     4 years    
Non-employee Consultants and Advisers | Unvested restricted common stock          
Class of Stock [Line Items]          
Restricted common stock, shares outstanding     12,860    
Restricted common stock, fair value of shares vested | $     $ 22,000 $ 71,000  
Issued, number of shares (shares)     0 18,194 0