Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Additional Information (Details)

v3.8.0.1
Stockholders' Equity - Additional Information (Details) - USD ($)
12 Months Ended
Aug. 10, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Class of Stock [Line Items]        
Common stock issuable upon preferred stock conversion (in shares) 1,667,683      
Common shares issuable upon conversion of warrants (in warrants) 1,250,764      
Common stock dividends   $ 0    
Series D and E Preferred Shares        
Class of Stock [Line Items]        
Deemed dividend to convertible preferred shareholders $ 24,900,000      
Convertible Preferred Stock        
Class of Stock [Line Items]        
Preferred Stock Shares Issued And Outstanding   0 0  
Preferred stock dividend declared or paid   $ 0 $ 0 $ 0
Initial Public Offering        
Class of Stock [Line Items]        
Common stock shares issued 17,900,000      
Sale of stock (in dollars per share) $ 14.00      
Proceeds from issuance initial public offering $ 220,900,000      
Offering expense $ 7,900,000      
Shares sold by shareholders in initial public offering (in shares) 417,732      
Convertible preferred stock into common stock (in shares) 54,840,767