Long Term Debt (Narrative) (Details) (USD $)	6 Months Ended	3 Months Ended						6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 E2 Investment [Member]	Jun. 30, 2013 CEI Credit Facility [Member] Post Amendment [Member]	Jun. 30, 2013 CEI Credit Facility [Member] Pre Amendment [Member]	Jun. 30, 2013 CEI Credit Facility [Member]	Jun. 30, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Jun. 30, 2013 Maximum [Member] Prior To December 31, 2013 [Member]	Jun. 30, 2013 Maximum [Member] December 31, 2013 And Thereafter [Member]	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Minimum [Member] September 30, 2013 And December 31, 2013 [Member]	Jun. 30, 2013 Minimum [Member] December 31, 2013 And Thereafter [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Initiation Date	Mar. 05, 2013
Line of Credit Facility, Maximum Borrowing Capacity			$ 90,000,000	$ 75,000,000		$ 635,000,000.0
Additional Investment Commitment in JV		25,000,000.0
Line of Credit Facility, Expiration Date	Mar. 05, 2016
Line of Credit Facility, Amount Outstanding					26,400,000	0	71,000,000
Line of Credit Facility, Remaining Borrowing Capacity					63,600,000	571,800,000
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%									42.50%
Letters of Credit Outstanding, Amount						63,200,000
Debt Instrument, Covenant Compliance, Additional Borrowing Capacity						$ 363,500,000
Interest Coverage Charge Ratios											2.25	2.50
Leverage Ratio, Consolidated								5.50	5.25