Annual report pursuant to Section 13 and 15(d)

Mandatorily-Redeemable Preferred Stock - Mandatorily-Redeemable Preferred Stock (Detail)

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Mandatorily-Redeemable Preferred Stock - Mandatorily-Redeemable Preferred Stock (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Aug. 17, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Mar. 31, 2017
Subsidiary, Sale of Stock [Line Items]          
Common stock, shares issued (in shares)   13,791,574 10,024,875    
Proceeds from issuance of mandatorily-redeemable preferred stock   $ 0 $ 28,750 $ 0  
Proceeds from issuance of equity   41,907 360 23,133  
Payments of legal costs   $ 1,977 $ 272 $ 1,482  
Over-Allotment Option          
Subsidiary, Sale of Stock [Line Items]          
Common stock, shares issued (in shares)         1,825,749
Series A cumulative term preferred stock          
Subsidiary, Sale of Stock [Line Items]          
Number of shares issued (in shares) 1,000,000        
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 equity $ 27,600        
Redemption price of redeemable preferred stock (in dollars per share) $ 25 $ 25.86      
Payments of legal costs $ 1,200        
Term preferred stock, fair value   $ 29,700      
Series A cumulative term preferred stock | Preferred Stock          
Subsidiary, Sale of Stock [Line Items]          
Proceeds from issuance of mandatorily-redeemable preferred stock $ 28,800        
Series A cumulative term preferred stock | Over-Allotment Option          
Subsidiary, Sale of Stock [Line Items]          
Number of shares issued (in shares) 150,000        
Series A cumulative term preferred stock | Universal Registration Statement One | Preferred Stock          
Subsidiary, Sale of Stock [Line Items]          
Common stock, shares issued (in shares)   1,150,000