Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Dividends Declared (Detail)

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Stockholders' Equity - Dividends Declared (Detail) - $ / shares
 3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
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 0.4688 0.4688 1.4063 1.4063
Series C Preferred Stock [Member]        
Dividends Payable [Line Items]        
Preferred Stock, distributions declared per share $ 0.4453 $ 0.4453 $ 1.3359 $ 1.3359