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 ($)
 1 Months Ended 9 Months Ended
Feb. 29, 2016
Sep. 30, 2016
Jun. 30, 2016
Dec. 31, 2015
Series D Cumulative Redeemable Preferred Stock [Member]        
Class of Stock [Line Items]        
Redeemable preferred stock, dividend rate percentage   7.00%    
Redeemable preferred stock, par value (in dollars per share)   $ 0.001    
Sale of stock, consideration received on transaction   $ 55,100,000    
Payments for repurchase of redeemable preferred stock   $ 38,500,000    
Temporary equity, contract terms, change in control threshold   50.00%    
Temporary equity, contract terms, minimum vote needed to trigger change in control from tender offer   90.00%    
Preferred Stock [Member]        
Class of Stock [Line Items]        
Redeemable preferred stock, shares issued (in shares)   2,264,000   2,150,000
Preferred Stock [Member] | Cantor Fitzgerald & Co [Member]        
Class of Stock [Line Items]        
Maximum remaining capacity to sell preferred stock under open market sale agreement   $ 37,200,000    
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 $ 40,000,000      
Redeemable preferred stock, dividend rate percentage 7.50%      
Redeemable preferred stock, shares issued (in shares)   114,000    
Preferred stock, net proceeds from offering   $ 2,800,000    
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     $ 50,000,000.0  
Maximum remaining capacity to sell preferred stock under open market sale agreement   $ 37,300,000    
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 $ 160,000,000      
Number of shares sold under open market sale agreement   65,000    
Net proceeds under ATM program   $ 900,000    
Maximum remaining capacity to sell preferred stock under open market sale agreement   $ 141,100,000    
Redeemable preferred stock, shares issued (in shares)   1,100,000    
Preferred stock, net proceeds from offering   $ 17,700,000    
Series D Preferred Stock ATM Program [Member] | Series D Cumulative Redeemable Preferred Stock [Member]        
Class of Stock [Line Items]        
Sale of stock, number of shares issued in transaction   502,000    
Sale of stock, consideration received on transaction   $ 12,500,000    
Private Placement [Member] | Series D Cumulative Redeemable Preferred Stock [Member]        
Class of Stock [Line Items]        
Sale of stock, number of shares issued in transaction   2,273,725    
Redeemable preferred stock, liquidation preference (in dollars per share)   $ 25.00