Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Dividends Declared (Detail)

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Stockholders' Equity - Dividends Declared (Detail) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dividends Payable [Line Items]        
Common Stock, distributions declared per share $ 0.375 $ 0.375 $ 1.125 $ 1.125
Common Stock [Member]
       
Dividends Payable [Line Items]        
Common Stock, distributions declared per share $ 0.375 $ 0.375 $ 1.125 $ 1.125
Senior Common Stock [Member]
       
Dividends Payable [Line Items]        
Common Stock, distributions declared per share $ 0.2625 $ 0.2625 $ 0.7875 $ 0.7875
Series A Preferred Stock [Member]
       
Dividends Payable [Line Items]        
Preferred Stock, distributions declared per share $ 0.4843749 $ 0.4843749 $ 1.4531247 $ 1.4531247
Series B Preferred Stock [Member]
       
Dividends Payable [Line Items]        
Preferred Stock, distributions declared per share $ 0.46875 $ 0.46875 $ 1.40630 $ 1.40630
Series C Preferred Stock [Member]
       
Dividends Payable [Line Items]        
Preferred Stock, distributions declared per share $ 0.4453125 $ 0.4453125 $ 1.3359000 $ 1.1875000