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Common Stock - Additional Information (Detail) - USD ($)
$ in Thousands
 1 Months Ended 6 Months Ended 9 Months Ended
Aug. 31, 2017
Jun. 30, 2017
Sep. 30, 2017
Dec. 31, 2016
Class Of Stock [Line Items]        
Common stock, shares outstanding     60,587,000 38,599,000
Proceeds from issuance of common stock, net     $ 169,187  
Underwritten Public Offering | Common Stock        
Class Of Stock [Line Items]        
Issuance of common stock (in shares) 5,750,000      
Net proceeds from Issuance public offering $ 80,800      
At the Market Sales Agreement        
Class Of Stock [Line Items]        
Issuance of common stock (in shares)   15,997,202    
Proceeds from issuance of common stock, net   $ 88,200    
Agreement Termination period   2017-06