Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.8.0.1
Stockholders' Equity - Additional Information (Detail)
$ in Thousands, shares in Millions
 1 Months Ended 3 Months Ended
Jan. 31, 2018
USD ($)
shares
Mar. 31, 2018
USD ($)
shares
Mar. 31, 2017
USD ($)
Class of Stock [Line Items]      
Conversion ratio   1  
Fees and commissions   $ 526 $ 135
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 | shares 1.5    
Fees and commissions $ 500    
Convertible Preferred Stock      
Class of Stock [Line Items]      
Convertible preferred stock, shares issued | shares   6.1  
Discharged amounts outstanding   $ 22,650  
Amounts to be invoiced   27,349  
Maximum | At-the-Market Program      
Class of Stock [Line Items]      
Aggregate purchase price, net of offering costs   $ 189,700