Annual report pursuant to Section 13 and 15(d)

Nature of Business (Details)

v3.8.0.1
Nature of Business (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Feb. 02, 2018
Apr. 26, 2017
Jul. 06, 2016
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jul. 07, 2016
Stock Offering                      
Common stock issued upon conversion of convertible preferred stock (in shares)     15,988,800                
Common stock, shares authorized (in shares)     200,000,000 200,000,000       200,000,000 200,000,000    
Preferred stock, shares authorized (in shares)     10,000,000 10,000,000       10,000,000 10,000,000    
Par value, common stock (in dollars per share)     $ 0.001 $ 0.001       $ 0.001 $ 0.001    
Par value, preferred stock (in dollars per share)     $ 0.001 $ 0.001       $ 0.001 $ 0.001    
Net loss       $ 10,965 $ 14,169 $ 12,021 $ 10,588 $ 54,010 $ 47,743 $ 29,818  
Accumulated deficit       $ 101,256       155,266 $ 101,256    
Cash equivalents and marketable securities               $ 72,000      
Convertible Preferred Stock                      
Stock Offering                      
Convertible preferred stock, shares outstanding (in shares)                     0
Over-allotment                      
Stock Offering                      
Shares issued 628,272                    
Common Stock                      
Stock Offering                      
Shares issued               2,592,591 4,600,000    
Common Stock | IPO                      
Stock Offering                      
Shares issued     4,600,000                
Share price (in dollars per share)     $ 12.50                
Aggregate gross proceeds     $ 57,500                
Net proceeds     49,900                
Underwriting discounts and commissions and offering costs     $ 7,600                
Common Stock | Over-allotment                      
Stock Offering                      
Shares issued     600,000                
Common Stock | Private Placement                      
Stock Offering                      
Shares issued   2,592,591                  
Share price (in dollars per share)   $ 13.50                  
Aggregate gross proceeds   $ 35,000                  
Placement agent fees   2,100                  
Other offering expenses   $ 300