Quarterly report pursuant to Section 13 or 15(d)

Subsequent Events - Monthly Distributions Declared by Company's Board of Directors (Detail)

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Subsequent Events - Monthly Distributions Declared by Company's Board of Directors (Detail) - Jul. 14, 2015 - Subsequent Event [Member] - $ / shares
Total
Senior Common Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.2625
Series A Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.4843749
Series B Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.4687500
Series C Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.4453125
Common Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.3750000
Installment 1 - FY2015 [Member]  
Dividends Payable [Line Items]  
Record Date Jul. 24, 2015
Payment Date Aug. 04, 2015
Installment 1 - FY2015 [Member] | Senior Common Stock [Member]  
Dividends Payable [Line Items]  
Payment Date Aug. 07, 2015
Distribution per Share $ 0.0875
Payable to the Holders of Records During the Month July
Installment 1 - FY2015 [Member] | Series A Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.1614583
Installment 1 - FY2015 [Member] | Series B Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.1562500
Installment 1 - FY2015 [Member] | Series C Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.1484375
Installment 1 - FY2015 [Member] | Common Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.1250000
Installment 2 - FY2015 [Member]  
Dividends Payable [Line Items]  
Record Date Aug. 20, 2015
Payment Date Aug. 31, 2015
Installment 2 - FY2015 [Member] | Senior Common Stock [Member]  
Dividends Payable [Line Items]  
Payment Date Sep. 08, 2015
Distribution per Share $ 0.0875
Payable to the Holders of Records During the Month August
Installment 2 - FY2015 [Member] | Series A Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.1614583
Installment 2 - FY2015 [Member] | Series B Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.1562500
Installment 2 - FY2015 [Member] | Series C Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.1484375
Installment 2 - FY2015 [Member] | Common Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.1250000
Installment 3 - FY2015 [Member]  
Dividends Payable [Line Items]  
Record Date Sep. 21, 2015
Payment Date Sep. 30, 2015
Installment 3 - FY2015 [Member] | Senior Common Stock [Member]  
Dividends Payable [Line Items]  
Payment Date Oct. 07, 2015
Distribution per Share $ 0.0875
Payable to the Holders of Records During the Month September
Installment 3 - FY2015 [Member] | Series A Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.1614583
Installment 3 - FY2015 [Member] | Series B Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.1562500
Installment 3 - FY2015 [Member] | Series C Preferred Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share 0.1484375
Installment 3 - FY2015 [Member] | Common Stock [Member]  
Dividends Payable [Line Items]  
Distribution per Share $ 0.1250000