Quarterly report pursuant to Section 13 or 15(d)

Nature of Business (Details)

v3.7.0.1
Nature of Business (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Jul. 06, 2016
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Jul. 07, 2016
Initial Public Offering              
Underwriting discounts, commissions and other offering costs     $ 1,427        
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      
Preferred stock, shares authorized (in shares) 10,000,000 10,000,000   10,000,000      
Par value, common stock (in dollars per share) $ 0.001 $ 0.001   $ 0.001      
Par value, preferred stock (in dollars per share)   $ 0.001   $ 0.001      
Net loss   $ 11,515 $ 10,588 $ 47,700 $ 29,800 $ 13,400  
Accumulated deficit   112,771   $ 101,256      
Cash equivalents and marketable securities   $ 70,500          
Convertible Preferred Stock              
Initial Public Offering              
Convertible preferred stock, shares outstanding (in shares)             0
Common Stock | IPO              
Initial Public 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, commissions and other offering costs $ 7,600            
Common Stock | Over-allotment              
Initial Public Offering              
Shares issued 600,000