Quarterly report pursuant to Section 13 or 15(d)

Stockholders' and Mezzanine Equity - Additional Information (Detail)

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Stockholders' and Mezzanine Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 6 Months Ended
Feb. 29, 2016
Feb. 29, 2012
Jun. 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 D Cumulative Redeemable Preferred Stock | Series D Preferred Stock ATM Program            
Class of Stock [Line Items]            
Number of shares issued (in shares)     300,000      
Consideration received     $ 6,900,000      
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)     900,000      
Net proceeds from offering     $ 17,900,000      
Maximum remaining capacity to sell preferred stock under open market sale agreement     $ 114,300,000      
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     $ 26,700,000