Quarterly report pursuant to Section 13 or 15(d)

Stockholders' and Mezzanine Equity - Dividends Paid (Detail)

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Stockholders' and Mezzanine Equity - Dividends Paid (Detail) - $ / shares
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Senior Common Stock        
Dividends Payable [Line Items]        
Common Stock, dividends paid per share $ 0.2625 $ 0.2625 $ 0.525 $ 0.525
Series A Preferred Stock        
Dividends Payable [Line Items]        
Preferred Stock, dividends paid per share 0.4843749 0.4843749 0.9687498 0.9687498
Series B Preferred Stock        
Dividends Payable [Line Items]        
Preferred Stock, dividends paid per share 0.46875 0.46875 0.9375 0.9375
Series D Preferred Stock        
Dividends Payable [Line Items]        
Preferred Stock, dividends paid per share 0.4374999 0.4374999 0.8749998 0.8749998
Common Stock        
Dividends Payable [Line Items]        
Common Stock, dividends paid per share $ 0.375 $ 0.375 $ 0.75 $ 0.75