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 6 Months Ended
Mar. 28, 2015
Mar. 31, 2011
Mar. 31, 2015
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2014
Sep. 02, 2014
Class of Stock [Line Items]              
Common stock, shares issued       21,143,986   19,589,606  
Common stock, par value       $ 0.001   $ 0.001  
Shares intended to be offered pursuant to primary offering   3,000,000          
Shares offered under distribution reinvestment plan   500,000          
Shares of senior common stock sold in offering 927,994   189,052        
Senior common stock offering, gross proceeds       $ 30,363,000 $ 36,042,000    
Repayment date of note including interest       May 07, 2015      
Senior Common Stock [Member]              
Class of Stock [Line Items]              
Common stock, shares issued   3,500,000          
Common stock, par value   $ 0.001          
Common stock shares issued, selling price   $ 15.00 $ 15.00        
Shares offered under distribution reinvestment plan 27,038   5,134        
Net proceeds after deducting underwriting discount and commission     $ 2,600,000        
Senior common stock offering, gross proceeds $ 13,900,000            
Cantor Fitzgerald & Co [Member]              
Class of Stock [Line Items]              
Maximum aggregate sales price of shares to be issued under open market sale agreement             $ 100,000,000
Net proceeds under ATM program       $ 27,200,000      
Number of shares sold under open market sale agreement       3,400,000      
Gross proceeds of shares sold under open market sale agreement       $ 60,100,000      
Maximum remaining capacity to sell common stock under open market sale agreement       $ 39,900,000