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Subsequent Events (Details) (USD $) In Thousands, except Share data, unless otherwise specified | 9 Months Ended | 0 Months Ended |
--- | --- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Oct. 17, 2012 Issuance of Equity [Member] | Oct. 16, 2012 Issuance of Equity [Member]
Subsequent Event [Line Items] |  |  |  |
Preferred shares issued to the public (in shares) and Common shares issued to the public (in shares) | 6,900,000 | 4,600,000 | 8,600,000 |
Public Offering, Price Per Share |  |  |  | $ 24.75
Public Offering, Proceeds After Underwriter Discounts But Before Offering Expenses | $ 165,662 | $ 145,361 | $ 204,900 |

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