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
 9 Months Ended
Sep. 30, 2017
Oct. 10, 2017
Sep. 30, 2016
10/31/2017      
Subsequent Event [Line Items]      
Record Date Oct. 20, 2017    
Payment Date Oct. 31, 2017    
11/30/2017      
Subsequent Event [Line Items]      
Record Date Nov. 20, 2017    
Payment Date Nov. 30, 2017    
12/29/2017      
Subsequent Event [Line Items]      
Record Date Dec. 19, 2017    
Payment Date Dec. 29, 2017    
Common Stock | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   $ 0.1323  
Common Stock | 10/31/2017 | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   0.0441  
Common Stock | 11/30/2017 | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   0.0441  
Common Stock | 12/29/2017 | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   0.0441  
Preferred Stock | Term Preferred Stock      
Subsequent Event [Line Items]      
Distributions per share $ 1.1953125   $ 0.190364583
Preferred Stock | Term Preferred Stock | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   0.3984375  
Preferred Stock | Term Preferred Stock | 10/31/2017 | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   0.1328125  
Preferred Stock | Term Preferred Stock | 11/30/2017 | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   0.1328125  
Preferred Stock | Term Preferred Stock | 12/29/2017 | Subsequent event      
Subsequent Event [Line Items]      
Distributions per share   $ 0.1328125