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 9 Months Ended
Jun. 24, 2013
Apr. 29, 2013
Mar. 31, 2011
Sep. 30, 2013
Sep. 30, 2012
Jul. 11, 2013
Dec. 31, 2012
Dividends Payable [Line Items]              
Common stock, shares issued       14,258,492     11,083,584
Gross proceeds of initial public offering $ 27,800,000 $ 23,900,000          
Net proceeds of initial public offering 26,300,000 22,600,000          
Underwriters' option to purchase additional shares of common stock           158,000  
Maximum aggregate sales price of shares to be issued under open market sale agreement       25,000,000      
Gross proceeds under ATM program       7,800,000      
Number of shares sold under open market sale agreement       762,478      
Net proceeds of shares sold under open market sale agreement       14,000,000      
Maximum remaining capacity to sell common stock under open market sale agreement       11,000,000      
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       62,139,000 1,103,000    
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       331,830      
Senior common stock ongoing offering, gross proceeds       $ 4,100,000      
Shares of senior common stock issued       6,741      
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