| Financial Instruments - Notional Amounts of Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended | 
|---|---|
| Dec. 31, 2012 | |
| Derivative [Line Items] | |
| Percentage of Debt Hedged by Interest Rate Derivatives | 75.00% | 
| Variable Rate Loan converted to Fixed Rate | $ 20.0 | 
| Notional Amount of Interest Rate Derivatives | 2,900.0 | 
| Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | |
| Derivative [Line Items] | |
| Derivative, Average Fixed Interest Rate | 1.98% | 
| Notional Amount of Interest Rate Derivatives | 0 | 
| Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | |
| Derivative [Line Items] | |
| Derivative, Average Fixed Interest Rate | 1.98% | 
| Notional Amount of Interest Rate Derivatives | 0 | 
| Maximum [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | |
| Derivative [Line Items] | |
| Notional Amount of Interest Rate Derivatives | 0 | 
| Maximum [Member] | Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member] | |
| Derivative [Line Items] | |
| Notional Amount of Interest Rate Derivatives | $ 0 | 
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- Definition The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Average fixed interest rate related to the group of interest rate derivatives. No definition available. 
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- Details 
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- Definition Aggregate notional amount of interest rate derivatives, which relates to the currency amount specified in the interest rate derivative instruments. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Percentage of an entity's outstanding debt that is designated as a hedged item in cash flow, fair value, or net investment hedge. No definition available. 
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