Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.3.1.900
Stockholders' Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Mar. 28, 2015
Mar. 31, 2011
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Class of Stock [Line Items]            
Capital gains       0.00% 0.00% 0.00%
Common stock, shares issued       22,485,607 19,589,606  
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        
Shares of senior common stock sold in offering 927,994   189,052      
Senior common stock offering, gross proceeds       $ 50,165,000 $ 73,931,000 $ 88,121,000
Outstanding Balance of Employee Loan         $ 375,000  
Employees [Member]            
Class of Stock [Line Items]            
Outstanding Balance of Employee Loan       0    
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    
Number of shares sold under open market sale agreement       4,800,000    
Net proceeds of shares sold under open market sale agreement       $ 80,000,000    
Maximum remaining capacity to sell common stock under open market sale agreement       20,000,000    
Net proceeds under ATM program       $ 46,700,000    
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 intended to be offered pursuant to senior common 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