Long Term Debt (Indebtedness Table) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Line of Credit [Member] | Twenty Sixteen [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 12,000,000	$ 71,000,000
Variable Interest Rate	3.30%	4.30%
Line of Credit [Member] | Twenty Eighteen [Member] | Eight Point Eight Seven Five Percent [Member]
Debt Instrument [Line Items]
Fixed Interest Rate		8.875%
Line of Credit [Member] | Twenty Twentytwo [Member] | Seven Point One Two Five Percent [Member]
Debt Instrument [Line Items]
Fixed Interest Rate		7.175%
Unsecured Debt [Member] | Twenty Eighteen [Member] | Eight Point Eight Seven Five Percent [Member]
Debt Instrument [Line Items]
Long-term Debt	715,780,000	715,305,000
Fixed Interest Rate	8.875%
Unamortized Discount on Debt	9,200,000	9,700,000
Unsecured Debt [Member] | Twenty Twentytwo [Member] | Seven Point One Two Five Percent [Member]
Debt Instrument [Line Items]
Long-term Debt	250,000,000	250,000,000
Fixed Interest Rate	7.175%
CEI Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt	22,000,000
CEI Credit Facility [Member] | Twenty Sixteen [Member]
Debt Instrument [Line Items]
Variable Interest Rate	5.30%
Total Debt [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 999,780,000	$ 1,036,305,000