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Asset Retirement Obligations (Details) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Asset Retirement Obligations [Line Items]    
Asset Retirement Obligations Assets Held-for-sale Noncurrent $ 3,033,000 $ 1,393,000
Asset Retirement Obligation, Current 2,500,000 6,200,000
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Asset Retirement Obligation: Beginning of Year 120,518,000 95,906,000
Asset Retirement Obligation, Liabilities Incurred 18,682,000 13,050,000
Asset Retirement Obligation, Liabilities Settled (33,129,000) (8,101,000)
Asset Retirement Obligation, Accretion Expense 5,997,000 4,679,000
Asset Retirement Obligation, Revision of Estimate 9,118,000 14,984,000
Asset Retirement Obligation: End of Year $ 121,186,000 $ 120,518,000
Minimum [Member]
   
Asset Retirement Obligations [Line Items]    
Asset Retirement Obligations, Assumptions Used, Risk Free Interest Rate 5.50%  
Maximum [Member]
   
Asset Retirement Obligations [Line Items]    
Asset Retirement Obligations, Assumptions Used, Risk Free Interest Rate 12.00%