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Stockholders' Equity and Mezzanine Equity - Dividends Declared (Detail) - $ / shares | 12 Months Ended
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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

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- Definition Aggregate dividends paid during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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