Quarterly report pursuant to Section 13 or 15(d)

Stockholders' and Mezzanine Equity - Additional Information (Detail)

v3.8.0.1
Stockholders' and Mezzanine Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 9 Months Ended
Jul. 31, 2017
Feb. 29, 2016
Feb. 29, 2012
Sep. 30, 2017
Jan. 11, 2017
Dec. 31, 2016
Jun. 30, 2016
Class of Stock [Line Items]              
Partnership units authorized (in shares)         0    
Mandatorily redeemable preferred stock              
Class of Stock [Line Items]              
Redeemable preferred stock, shares issued (in shares)     1,540,000        
Series A and B Preferred Stock ATM Programs              
Class of Stock [Line Items]              
Redeemable preferred stock, shares issued (in shares)       2,264,000   2,264,000  
Redeemable preferred stock (in shares)       5,350,000   5,350,000  
Series D Cumulative Redeemable Preferred Stock              
Class of Stock [Line Items]              
Redeemable preferred stock, dividend rate percentage (as percent)       7.00%      
Temporary equity, contract terms, minimum vote needed to trigger change in control from tender offer (as percent)       90.00%      
Series C Preferred Stock              
Class of Stock [Line Items]              
Redeemable preferred stock, dividend rate percentage (as percent)     7.125%        
Series C Preferred Stock | Mandatorily redeemable preferred stock              
Class of Stock [Line Items]              
Redeemable preferred stock (in shares)         0 160,000  
Cantor Fitzgerald & Co | Common Stock              
Class of Stock [Line Items]              
Maximum aggregate sales price of shares to be issued under open market sale agreement   $ 160,000,000.0          
Redeemable preferred stock, shares issued (in shares)       1,500,000      
Net proceeds from offering       $ 30,800,000      
Maximum remaining capacity to sell preferred stock under open market sale agreement       $ 101,100,000      
Cantor Fitzgerald & Co | Preferred Stock | Series A and B Preferred Stock ATM Programs              
Class of Stock [Line Items]              
Redeemable preferred stock, shares issued (in shares)       0      
Maximum remaining capacity to sell preferred stock under open market sale agreement       $ 37,200,000      
Cantor Fitzgerald & Co | Preferred Stock | Series A Cumulative Redeemable Preferred Stock              
Class of Stock [Line Items]              
Redeemable preferred stock, dividend rate percentage (as percent)   7.75%          
Cantor Fitzgerald & Co | Preferred Stock | Series B Cumulative Redeemable Preferred Stock              
Class of Stock [Line Items]              
Maximum aggregate sales price of shares to be issued under open market sale agreement   $ 40,000,000.0          
Redeemable preferred stock, dividend rate percentage (as percent)   7.50%          
Cantor Fitzgerald & Co | Preferred Stock | Series D Cumulative Redeemable Preferred Stock              
Class of Stock [Line Items]              
Maximum aggregate sales price of shares to be issued under open market sale agreement             $ 50,000,000.0
Maximum remaining capacity to sell preferred stock under open market sale agreement       $ 22,300,000      
Overnight Offering              
Class of Stock [Line Items]              
Number of shares issued (in shares) 1,200,000            
Offering price (in dollars per share) $ 20.52            
Consideration received $ 22,700,000            
Over-Allotment Option              
Class of Stock [Line Items]              
Number of shares issued (in shares) 200,000            
Offering price (in dollars per share) $ 20.52            
Consideration received $ 3,400,000            
Series D Preferred Stock ATM Program | Series D Cumulative Redeemable Preferred Stock              
Class of Stock [Line Items]              
Number of shares issued (in shares)       400,000      
Consideration received       $ 11,200,000