Annual report pursuant to Section 13 and 15(d)

Mandatorily-Redeemable Preferred Stock (Detail)

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Mandatorily-Redeemable Preferred Stock (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 12 Months Ended
Aug. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Sale of Stock [Line Items]      
Common stock, shares issued (in shares)   17,891,340 13,791,574
Proceeds from issuance of preferred and common equity   $ 74,417 $ 41,907
Payments of legal costs   $ 4,186 $ 1,977
Series A Preferred Stock      
Sale of Stock [Line Items]      
Preferred stock, dividend rate (as percent) 6.375%    
Preferred stock, par value (in dollars per share) $ 0.001 $ 0.001 $ 0.001
Public offering price (in dollars per share) $ 25    
Proceeds from issuance of preferred and common equity $ 27,600    
Redemption price of redeemable preferred stock (in dollars per share) $ 25 $ 25.47  
Payments of legal costs $ 1,200    
Term preferred stock, fair value   $ 29,300  
Series A Preferred Stock | Preferred Stock      
Sale of Stock [Line Items]      
Common stock, shares issued (in shares) 1,150,000    
Proceeds from issuance of mandatorily-redeemable preferred stock $ 28,800