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Financial Instruments (Details) (USD $)
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12 Months Ended | |
|---|---|---|
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Dec. 31, 2011
gal
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Dec. 31, 2010
gal
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Fuel Hedges Contract Three [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Nov. 05, 2007 | Nov. 05, 2007 |
| Commencement Date | Jan. 05, 2009 | Jan. 05, 2009 |
| Termination Date | Dec. 30, 2013 | Dec. 30, 2013 |
| Notional Amount (in Gallons per Month) | 60,000 | 60,000 |
| Contract Price Per Gallon | $ 3.28 | $ 3.28 |
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Fuel Hedges Contract Four [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Mar. 17, 2008 | Mar. 17, 2008 |
| Commencement Date | Jan. 05, 2009 | Jan. 05, 2009 |
| Termination Date | Dec. 31, 2012 | Dec. 31, 2012 |
| Notional Amount (in Gallons per Month) | 50,000 | 50,000 |
| Contract Price Per Gallon | 3.72 | 3.72 |
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Fuel Hedges Contract Five [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Mar. 17, 2008 | Mar. 17, 2008 |
| Commencement Date | Jan. 05, 2009 | Jan. 05, 2009 |
| Termination Date | Dec. 31, 2012 | Dec. 31, 2012 |
| Notional Amount (in Gallons per Month) | 50,000 | 50,000 |
| Contract Price Per Gallon | 3.74 | 3.74 |
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Fuel Hedges Contract Six [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Sep. 22, 2008 | Sep. 22, 2008 |
| Commencement Date | Jan. 01, 2009 | Jan. 01, 2009 |
| Termination Date | Dec. 31, 2011 | Dec. 31, 2011 |
| Notional Amount (in Gallons per Month) | 150,000 | 150,000 |
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Fuel Hedges Contract Six [Member] | Minimum [Member]
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| Summary of outstanding hedges | ||
| Contract Price Per Gallon | 4.16 | 4.16 |
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Fuel Hedges Contract Six [Member] | Maximum [Member]
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| Summary of outstanding hedges | ||
| Contract Price Per Gallon | 4.17 | 4.17 |
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Fuel Hedges Contract Eight [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Jul. 10, 2009 | Jul. 10, 2009 |
| Commencement Date | Jan. 01, 2011 | Jan. 01, 2011 |
| Termination Date | Dec. 31, 2011 | Dec. 31, 2011 |
| Notional Amount (in Gallons per Month) | 100,000 | 100,000 |
| Contract Price Per Gallon | 3.05 | 3.05 |
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Fuel Hedges Contract Nine [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Jul. 10, 2009 | Jul. 10, 2009 |
| Commencement Date | Jan. 01, 2012 | Jan. 01, 2012 |
| Termination Date | Dec. 31, 2012 | Dec. 31, 2012 |
| Notional Amount (in Gallons per Month) | 100,000 | 100,000 |
| Contract Price Per Gallon | 3.20 | 3.20 |
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Fuel Hedges Contract Ten [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 08, 2011 | Aug. 08, 2011 |
| Commencement Date | Jul. 01, 2012 | Jul. 01, 2012 |
| Termination Date | Dec. 31, 2012 | Dec. 31, 2012 |
| Notional Amount (in Gallons per Month) | 500,000 | 500,000 |
| Contract Price Per Gallon | 3.84 | 3.84 |
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Fuel Hedges Contract Eleven [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 08, 2011 | Aug. 08, 2011 |
| Commencement Date | Jan. 01, 2013 | Jan. 01, 2013 |
| Termination Date | Dec. 31, 2013 | Dec. 31, 2013 |
| Notional Amount (in Gallons per Month) | 500,000 | 500,000 |
| Contract Price Per Gallon | 3.83 | 3.83 |
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Fuel Hedges Contract Twelve [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 08, 2011 | Aug. 08, 2011 |
| Commencement Date | Jan. 01, 2014 | Jan. 01, 2014 |
| Termination Date | Dec. 31, 2014 | Dec. 31, 2014 |
| Notional Amount (in Gallons per Month) | 500,000 | 500,000 |
| Contract Price Per Gallon | 3.82 | 3.82 |
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Fuel Hedges Contract Thirteen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 08, 2011 | Aug. 08, 2011 |
| Commencement Date | Jul. 02, 2012 | Jul. 02, 2012 |
| Termination Date | Dec. 31, 2012 | Dec. 31, 2012 |
| Notional Amount (in Gallons per Month) | 500,000 | 500,000 |
| Contract Price Per Gallon | 3.84 | 3.84 |
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Fuel Hedges Contract Fourteen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 08, 2011 | Aug. 08, 2011 |
| Commencement Date | Jan. 07, 2013 | Jan. 07, 2013 |
| Termination Date | Dec. 30, 2013 | Dec. 30, 2013 |
| Notional Amount (in Gallons per Month) | 500,000 | 500,000 |
| Contract Price Per Gallon | 3.82 | 3.82 |
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Fuel Hedges Contract Fifteen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 09, 2011 | Aug. 09, 2011 |
| Commencement Date | Jul. 01, 2012 | Jul. 01, 2012 |
| Termination Date | Dec. 31, 2012 | Dec. 31, 2012 |
| Notional Amount (in Gallons per Month) | 250,000 | 250,000 |
| Contract Price Per Gallon | 3.80 | 3.80 |
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Fuel Hedges Contract Sixteen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 09, 2011 | Aug. 09, 2011 |
| Commencement Date | Jan. 01, 2013 | Jan. 01, 2013 |
| Termination Date | Dec. 31, 2013 | Dec. 31, 2013 |
| Notional Amount (in Gallons per Month) | 250,000 | 250,000 |
| Contract Price Per Gallon | 3.83 | 3.83 |
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Fuel Hedges Contract Seventeen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 09, 2011 | Aug. 09, 2011 |
| Commencement Date | Jan. 01, 2014 | Jan. 01, 2014 |
| Termination Date | Dec. 31, 2014 | Dec. 31, 2014 |
| Notional Amount (in Gallons per Month) | 250,000 | 250,000 |
| Contract Price Per Gallon | 3.82 | 3.82 |
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Fuel Hedges Contract Eighteen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Aug. 09, 2011 | Aug. 09, 2011 |
| Commencement Date | Jan. 06, 2014 | Jan. 06, 2014 |
| Termination Date | Dec. 29, 2014 | Dec. 29, 2014 |
| Notional Amount (in Gallons per Month) | 500,000 | 500,000 |
| Contract Price Per Gallon | 3.83 | 3.83 |
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Fuel Hedges Contract Nineteen [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Sep. 30, 2011 | Sep. 30, 2011 |
| Commencement Date | Jan. 06, 2014 | Jan. 06, 2014 |
| Termination Date | Dec. 29, 2014 | Dec. 29, 2014 |
| Notional Amount (in Gallons per Month) | 250,000 | 250,000 |
| Contract Price Per Gallon | 3.69 | 3.69 |
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Fuel Hedges Contract Twenty [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Sep. 30, 2011 | Sep. 30, 2011 |
| Commencement Date | Jan. 07, 2013 | Jan. 07, 2013 |
| Termination Date | Dec. 30, 2013 | Dec. 30, 2013 |
| Notional Amount (in Gallons per Month) | 250,000 | 250,000 |
| Contract Price Per Gallon | 3.70 | 3.70 |
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Fuel Hedges Contract Twenty One [Member]
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| Summary of outstanding hedges | ||
| Inception Date | Oct. 03, 2011 | Oct. 03, 2011 |
| Commencement Date | Jan. 05, 2015 | Jan. 05, 2015 |
| Termination Date | Dec. 28, 2015 | Dec. 28, 2015 |
| Notional Amount (in Gallons per Month) | 250,000 | 250,000 |
| Contract Price Per Gallon | $ 3.68 | $ 3.68 |