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 3 Months Ended
Mar. 31, 2011
Mar. 31, 2014
Mar. 31, 2013
Dec. 31, 2013
Dividends Payable [Line Items]        
Maximum aggregate sales price of shares to be issued under open market sale agreement   $ 25,000,000    
Net proceeds under ATM program   7,200,000    
Number of shares sold under open market sale agreement   1,200,000    
Gross proceeds of shares sold under open market sale agreement   21,400,000    
Maximum remaining capacity to sell common stock under open market sale agreement   3,600,000    
Common stock, shares issued   16,081,365   15,662,414
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   7,707,000 6,484,000  
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   333,604    
Senior common stock ongoing offering, gross proceeds   $ 5,000,000    
Shares of senior common stock issued   12,047