Quarterly report pursuant to Section 13 or 15(d)

Stockholders' and Mezzanine Equity - Additional Information (Detail)

v3.5.0.2
Stockholders' and Mezzanine Equity - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
 1 Months Ended 6 Months Ended
Jun. 30, 2016
May 31, 2016
Feb. 29, 2016
Jun. 30, 2016
Dec. 31, 2015
Class of Stock [Line Items]          
Redeemable preferred stock, shares issued 2,264,000     2,264,000 2,150,000
Payments for Repurchase of Redeemable Preferred Stock $ 25.0     $ 25.0  
Series D Cumulative Redeemable Preferred Stock [Member]          
Class of Stock [Line Items]          
Redeemable preferred stock, shares issued 20,000     20,000  
Cantor Fitzgerald & Co [Member] | Series D Cumulative Redeemable Preferred Stock [Member]          
Class of Stock [Line Items]          
Redeemable preferred stock, dividend rate percentage     7.00%    
Preferred Stock [Member]          
Class of Stock [Line Items]          
Redeemable preferred stock, shares issued 2,264,000     2,264,000 2,150,000
Preferred Stock [Member] | Series D Cumulative Redeemable Preferred Stock [Member]          
Class of Stock [Line Items]          
Redeemable preferred stock, shares authorized   1,043,725      
Redeemable preferred stock, dividend rate percentage   7.00%      
Redeemable preferred stock, par value (in dollars per share)   $ 0.001      
Redeemable preferred stock, liquidation preference (in dollars per share)   $ 25.00      
Preferred Stock, Net Proceeds from Offering   $ 25.3   $ 0.5  
Preferred Stock [Member] | Cantor Fitzgerald & Co [Member]          
Class of Stock [Line Items]          
Maximum remaining capacity to sell preferred stock under open market sale agreement $ 37.2     $ 37.2  
Preferred Stock [Member] | Cantor Fitzgerald & Co [Member] | Series A Cumulative Redeemable Preferred Stock [Member]          
Class of Stock [Line Items]          
Redeemable preferred stock, dividend rate percentage     7.75%    
Preferred Stock [Member] | Cantor Fitzgerald & Co [Member] | Series B Cumulative Redeemable Preferred Stock [Member]          
Class of Stock [Line Items]          
Maximum aggregate sales price of shares to be issued under open market sale agreement     $ 40.0    
Redeemable preferred stock, dividend rate percentage     7.50%    
Redeemable preferred stock, shares issued 114,000     114,000  
Preferred Stock, Net Proceeds from Offering       $ 2.8  
Preferred Stock [Member] | Cantor Fitzgerald & Co [Member] | Series D Cumulative Redeemable Preferred Stock [Member]          
Class of Stock [Line Items]          
Maximum aggregate sales price of shares to be issued under open market sale agreement     $ 50.0    
Maximum remaining capacity to sell preferred stock under open market sale agreement $ 49.5     $ 49.5  
Common Stock [Member] | Cantor Fitzgerald & Co [Member]          
Class of Stock [Line Items]          
Maximum aggregate sales price of shares to be issued under open market sale agreement     $ 160.0    
Number of shares sold under open market sale agreement 65,000     65,000  
Net proceeds under ATM program       $ 0.9  
Maximum remaining capacity to sell preferred stock under open market sale agreement $ 151.8     $ 151.8  
Redeemable preferred stock, shares issued 433,000     433,000  
Preferred Stock, Net Proceeds from Offering       $ 7.2