Debt 4.00% Junior Subordinated Convertible Debentures (Details) (Junior Subordinated Convertible Debentures [Member], USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Junior Subordinated Convertible Debentures [Member]
Maximum aggregate liquidation amount offered	$ 345,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Remaining Liquidation Amount of Old Trust Piers	11,233,050
Debt Instrument, Convertible, Conversion Price	$ 40.82
Percent stock price closes above conversion price for option of conversion	130.00%
Percent threshold for average closing share price to enable option of conversion	105.00%
Percent threshold for average closing share price to enable option of conversion after maturity	98.00%
Percent threshold average share price after stated period to allow cash distribution	115.00%
Percent of share price cash distribution is based on	12.50%
Deferred Finance Costs, Gross	6,100,000
Amortization of Financing Costs	$ 200,000	$ 200,000	$ 200,000

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% of share price cash distribution is based on

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Remaining Liquidation Amount of Old Trust Piers

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- Definition

Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 8

-Article 9

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The price per share of the conversion feature embedded in the debt instrument.

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Interest rate stated in the contractual debt agreement.

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For an unclassified balance sheet, the amount as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain. Such amount is before the consideration of accumulated amortization.

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-Name Accounting Principles Board Opinion (APB)

-Number 21

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