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Senior Unsecured Notes (Narrative) (Details) (USD $)
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12 Months Ended |
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Dec. 31, 2012
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| Proceeds from the sale of senior unsecured notes | $ 547,926,000 |
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4.50% Senior Unsecured Notes, Due April 18, 2022 [Member]
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| Face amount of senior unsecured notes | 300,000,000 |
| Interest rate of senior unsecured notes | 4.50% |
| Mortgage loan, maturity date | Apr. 18, 2022 |
| Proceeds from the sale of senior unsecured notes | 296,800,000 |
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2.50% Senior Unsecured Notes, Due December 15, 2017 [Member]
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| Face amount of senior unsecured notes | 250,000,000 |
| Interest rate of senior unsecured notes | 2.50% |
| Mortgage loan, maturity date | Dec. 15, 2017 |
| Proceeds from the sale of senior unsecured notes | $ 246,400,000 |
| X | ||||||||||
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- Definition
The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Interest rate stated in the contractual debt agreement. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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