Long-Term Debt (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date	Mar. 05, 2016
Long-term Debt	$ 1,200,472,000	$ 1,036,305,000
Line Of Credit Facility Collateral Units	10,700,000
Line Of Credit Facility Base Interest Rate	5.00%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.75%
Line Of Credit Facility Loan To Equity Value Percentage	47.00%
CEI Credit Facility [Member] | Post Amendment [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	90,000,000.0
CEI Credit Facility [Member] | Pre Amendment [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75,000,000.0
CEI Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term Debt	65,041,000
Line of Credit Facility, Remaining Borrowing Capacity	25,000,000
Other Debt Obligations [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Initiation Date	Sep. 04, 2013
Line of Credit Facility, Maximum Borrowing Capacity	20,000,000
Line of Credit Facility, Interest Rate at Period End	4.159%
Line of Credit Facility, Expiration Date	Sep. 04, 2016
Line of Credit Facility, Amount Outstanding	12,700,000
Notes Payable, Noncurrent	500,000
Notes Payable, Maturity Date	Jul. 01, 2017
Notes Payable, Interest Rate, Stated Percentage Rate Range, Minimum	3.90%
Notes Payable, Interest Rate, Stated Percentage Rate Range, Maximum	7.00%
Long-term Debt	13,229,000
Line of Credit Facility, Remaining Borrowing Capacity	7,300,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Available Additional Borrowings	207,100,000
Line of Credit Facility, Maximum Borrowing Capacity	635,000,000
Line of Credit Facility, Amount Outstanding	59,700,000.0
Line of Credit Facility, Remaining Borrowing Capacity	420,300,000
Minimum [Member]
Line of Credit Facility [Line Items]
Line Of Credit Facility Loan To Equity Value Percentage	42.50%
2016 | CEI Credit Facility [Member]
Line of Credit Facility [Line Items]
Long-term Debt		0
2016 | Other Debt Obligations [Member]
Line of Credit Facility [Line Items]
Long-term Debt		$ 0