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Derivatives and Hedging (Details) (Interest Rate Swap, USD $) In Millions, unless otherwise specified |  | 12 Months Ended |  | 12 Months Ended |
--- | --- | --- | --- | --- | ---
Jun. 30, 2007 Derivative_Agreement | Dec. 31, 2012 Interest Rate Swap 1 | Mar. 31, 2010 Interest Rate Swap 1 | Dec. 31, 2012 Interst Rate Swap 2 | Mar. 31, 2011 Interst Rate Swap 2
Derivative [Line Items] |  |  |  |  |
Number of interest rate swap agreements | 2 |  |  |  |
Number of years in term for interest rate swap agreements |  | 3 years |  | 4 years |
Fixed LIBOR base rate |  |  | 4.91% |  | 4.935%
Notional amount of interest rate derivatives |  |  | $ 20 |  | $ 20

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