Quarterly report pursuant to Section 13 or 15(d)

Subsequent Events - Monthly Distributions Declared by Company's Board of Directors (Detail)

v3.8.0.1
Subsequent Events - Monthly Distributions Declared by Company's Board of Directors (Detail) - $ / shares
Jun. 29, 2018
Jun. 20, 2018
May 31, 2018
May 22, 2018
Apr. 30, 2018
Apr. 20, 2018
Apr. 10, 2018
Mar. 31, 2018
Mar. 31, 2017
4/30/2018 | Subsequent event                  
Subsequent Event [Line Items]                  
Record Date           Apr. 20, 2018      
Payment Date         Apr. 30, 2018        
Common Stock | Subsequent event                  
Subsequent Event [Line Items]                  
Distributions per share             $ 0.1329    
Common Stock | 4/30/2018 | Subsequent event                  
Subsequent Event [Line Items]                  
Distributions per share         $ 0.0443        
Preferred Stock | Term Preferred Stock                  
Subsequent Event [Line Items]                  
Distributions per share               $ 0.3984375 $ 0.3984375
Preferred Stock | Term Preferred Stock | Subsequent event                  
Subsequent Event [Line Items]                  
Distributions per share             $ 0.3984375    
Preferred Stock | Term Preferred Stock | 4/30/2018                  
Subsequent Event [Line Items]                  
Distributions per share               0.1328125 0.1328125
Preferred Stock | Term Preferred Stock | 4/30/2018 | Subsequent event                  
Subsequent Event [Line Items]                  
Distributions per share         $ 0.1328125        
Preferred Stock | Term Preferred Stock | 5/31/2018                  
Subsequent Event [Line Items]                  
Distributions per share               0.1328125 0.1328125
Preferred Stock | Term Preferred Stock | 6/29/2018                  
Subsequent Event [Line Items]                  
Distributions per share               $ 0.1328125 $ 0.1328125
Forecast | 5/31/2018                  
Subsequent Event [Line Items]                  
Record Date       May 22, 2018          
Payment Date     May 31, 2018            
Forecast | 6/29/2018                  
Subsequent Event [Line Items]                  
Record Date   Jun. 20, 2018              
Payment Date Jun. 29, 2018                
Forecast | Common Stock | 5/31/2018                  
Subsequent Event [Line Items]                  
Distributions per share     $ 0.0443            
Forecast | Common Stock | 6/29/2018                  
Subsequent Event [Line Items]                  
Distributions per share $ 0.0443                
Forecast | Preferred Stock | Term Preferred Stock | 5/31/2018                  
Subsequent Event [Line Items]                  
Distributions per share     $ 0.1328125            
Forecast | Preferred Stock | Term Preferred Stock | 6/29/2018                  
Subsequent Event [Line Items]                  
Distributions per share $ 0.1328125