Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity and Mezzanine Equity - Dividends Declared (Detail)

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Stockholders' Equity and Mezzanine Equity - Dividends Declared (Detail) - $ / shares
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Senior Common Stock      
Dividends Payable [Line Items]      
Common stock, cash paid (in dollars per share) $ 1.0500 $ 1.0500 $ 1.0500
Series A Preferred Stock      
Dividends Payable [Line Items]      
Preferred stock, cash paid (in dollars per share) 1.9374996 1.9374996 1.9374996
Series B Preferred Stock      
Dividends Payable [Line Items]      
Preferred stock, cash paid (in dollars per share) 1.8750 1.8750 1.8750
Series C Preferred Stock      
Dividends Payable [Line Items]      
Preferred stock, cash paid (in dollars per share) 0.0000 1.1330 1.7813
Series D Preferred Stock      
Dividends Payable [Line Items]      
Preferred stock, cash paid (in dollars per share) 1.7500 1.0538 0.0000
Common Stock      
Dividends Payable [Line Items]      
Common stock, cash paid (in dollars per share) $ 1.500 $ 1.500 $ 1.500