v2.4.0.6

Shareholders' Equity (Details) (USD $) | 0 Months Ended | 3 Months Ended | 0 Months Ended | 1 Months Ended | 3 Months Ended |  | 1 Months Ended | 3 Months Ended |  | 0 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2012 | Feb. 22, 2012 | Mar. 31, 2012 | Mar. 31, 2011 | Mar. 15, 2012 Common Stock [Member] | Dec. 31, 2006 Series D Preferred Stock [Member] | Mar. 31, 2012 Series D Preferred Stock [Member] | Nov. 30, 2011 Series D Preferred Stock [Member] | Mar. 31, 2004 Series C Preferred Stock [Member] | Mar. 31, 2012 Series C Preferred Stock [Member] | Mar. 23, 2009 Series C Preferred Stock [Member] | Nov. 17, 2010 Series B Preferred Stock [Member]
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Dividends declared, Per common share |  |  | $ 0.27 | $ 0.26 | $ 0.27 |  |  |  |  |  |  |
Dividends paid, Per common share |  |  |  |  | $ 0.27 |  |  |  |  |  |  |
Share repurchase program, Shares repurchased |  |  | 50,620 |  |  |  |  |  |  |  |  |
Shares repurchased during period, Aggregate value |  |  | $ (3,600,000) |  |  |  |  |  |  |  |  |
Shares repurchased during period, Average cost per share |  |  | $ 71.81 |  |  |  |  |  |  |  |  |
Share repurchase program, Authorized aggregate amount |  | 500,000,000 |  |  |  |  |  |  |  |  |  |
Share repurchase program, Remaining authorized aggregate amount | 500,000,000 |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of preference shares |  |  |  |  |  | 300,000,000 |  |  | 250,000,000 |  |  |
Preference shares issued, Shares |  |  |  |  |  | 12,000,000 |  |  | 10,000,000 |  |  |
Preference shares issued, Issuance price per share |  |  |  |  |  | $ 25 |  |  | $ 25 |  |  |
Preference shares, Dividend rate |  |  |  |  |  |  | 6.60% |  |  | 6.08% |  | 7.30%
Preference shares, Redemption price per share |  |  |  |  |  |  |  | $ 25 |  |  | $ 25 | $ 25
Dividends declared and paid, Preference shares |  |  | $ 8,750,000 | $ 8,750,000 |  |  |  |  |  |  |  |

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