Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

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Stockholders' Equity - Additional Information (Detail) (USD $)
 1 Months Ended 6 Months Ended
Jun. 24, 2013
Apr. 29, 2013
Mar. 31, 2011
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Dividends Payable [Line Items]            
Common stock, shares issued       14,017,648   14,017,648
Gross proceeds of initial public offering $ 24,800,000 $ 23,900,000        
Net proceeds of initial public offering 23,500,000 22,600,000        
Maximum aggregate sales price of shares to be issued under open market sale agreement       25,000,000    
Gross proceeds under ATM program       6,300,000    
Number of shares sold under open market sale agreement       665,994    
Net proceeds of shares sold under open market sale agreement       12,400,000    
Maximum remaining capacity to sell common stock under open market sale agreement       12,600,000    
Common stock, par value       $ 0.001   $ 0.001
Shares intended to be offered pursuant to primary offering     3,000,000      
Shares intended to be offered pursuant to senior common distribution reinvestment plan     500,000      
Senior common stock ongoing offering, gross proceeds       57,219,000 522,000  
Senior Common Stock [Member]
            
Dividends Payable [Line Items]            
Common stock, shares issued     3,500,000      
Common stock, par value     $ 0.001      
Common stock shares issued, selling price     $ 15.00      
Shares of senior common stock sold in ongoing offering       243,075    
Senior common stock ongoing offering, gross proceeds       $ 3,600,000    
Shares of senior common stock issued       4,527    
Public offering [Member]
            
Dividends Payable [Line Items]            
Common stock, shares issued 1,320,000 1,265,000        
Public offering price per share $ 18.82 $ 18.90