XML 79 R63.htm IDEA: XBRL DOCUMENT v3.19.1
Common Stock, Redeemable Common Stock, and Convertible Preferred Stock - Additional Information (Detail)
 1 Months Ended 3 Months Ended 12 Months Ended
Aug. 31, 2015
USD ($)
$ / shares
shares
Mar. 31, 2019
USD ($)
Directors
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Common stock, authorized shares   33,333,333 11,070,776
Common stock, par value | $ / shares   $ 0.001 $ 0.001
Common stock, voting right   Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company's stockholders. The holders of common stock, voting exclusively and as a separate class, are entitled to elect one director of the Company.  
Number of directors entitled to be elected | Directors   1  
Dividends on common stock declared or paid | $   $ 0 $ 0
Convertible preferred stock, shares authorized     49,413,523
Preferred stock outstanding | $   $ 0  
Genzyme Agreement [Member]      
Stock issued during period 107,371    
Common stock aggregate fair value | $ $ 734,000    
Common stock repurchase price per share | $ / shares $ 0.01    
Series Seed Preferred Stock [Member]      
Convertible preferred stock, shares authorized   10,000,000 59,413,523
Convertible preferred stock, par or stated value per share | $ / shares   $ 0.001 $ 0.001