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Common Stock - Additional Information (Detail) - USD ($)
6 Months Ended
Nov. 12, 2015
Jun. 30, 2017
Dec. 31, 2016
Class Of Stock [Line Items]      
Common stock, shares outstanding   54,747,656 38,599,000
Proceeds from issuance of common stock, net   $ 88,200,000  
Agreement Termination period   2017-06  
Cowen      
Class Of Stock [Line Items]      
Proceeds from issuance of common stock, net   $ 88,200,000  
Issuance of common stock (in shares)   15,997,202  
Maximum | Cowen      
Class Of Stock [Line Items]      
Common stock sales agreement aggregate sales proceeds $ 90,000,000