Shareholders' Equity (Summary of Dividends) (Details) - $ / shares	3 Months Ended	12 Months Ended
Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Dividends [Line Items]
Series 1 Cumulative Convertible Preferred Shares Interest Rate	5.417%		5.417%
Common shares
Dividends [Line Items]
Dividends declared per common share	$ 0.94	$ 0.87
Dividends paid per common share	$ 0.94	$ 0.87
5.417% Series 1 Cumulative Convertible Preferred shares
Dividends [Line Items]
Series 1 Cumulative Convertible Preferred Shares Interest Rate	5.417%	5.417%
Dividends declared per preferred share	$ 0.339	$ 0.339
Dividends paid per preferred share	$ 0.339	$ 0.339

[Line Items] for Dividends [Table]

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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

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Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

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The percentage rate used to calculate dividend payments on preferred stock.

+ References

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Aggregate dividends paid during the period for each share of preferred stock outstanding.

+ References

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Aggregate dividends declared during the period for each share of preferred stock outstanding.

+ References

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