Public Offering of units and Certain Provisions of the Partnership Agreement (Incentive Distributions) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Partners' Capital Notes [Abstract]
Income allocation for incentive distributions	$ 4,489	$ 2,372	$ 99
Stock-based compensation attributable to CEI's restricted shares	(4,205)	(3,119)	(3,906)
General partner interest in net income (loss)	(818)	15	(564)
General partner interest in net income (loss)	$ (534)	$ (732)	$ (4,371)