Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

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Stockholders' Equity - Additional Information (Detail)
$ in Thousands, shares in Millions
 1 Months Ended 3 Months Ended 9 Months Ended
Jun. 30, 2018
USD ($)
shares
Jan. 31, 2018
USD ($)
shares
Sep. 30, 2018
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Mar. 31, 2018
USD ($)
shares
Class of Stock [Line Items]            
Aggregate purchase price, net of offering costs $ 115,200          
Conversion ratio       1    
Option to purchase additional shares of common stock (in shares) | shares 12.0          
Fees and commissions $ 3,600     $ 4,090 $ 607  
Over-allotment Option            
Class of Stock [Line Items]            
Aggregate purchase price, net of offering costs   $ 14,500        
Option to purchase additional shares of common stock (in shares) | shares 1.8 1.5        
Fees and commissions   $ 500        
Convertible Preferred Stock            
Class of Stock [Line Items]            
Convertible preferred stock, shares issued (in shares) | shares           6.1
Discharged amounts outstanding           $ 22,700
Amounts to be invoiced           $ 27,300
Maximum | At-the-Market Program            
Class of Stock [Line Items]            
Aggregate purchase price, net of offering costs       189,700    
Other Noncurrent Assets            
Class of Stock [Line Items]            
Detailed engineering costs recognized     $ 12,500 $ 25,000    
Issuance of remaining preferred stock     $ 2,300