Employee Incentive Plans (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended								0 Months Ended		0 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2012 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2011 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2013 Share [Member]	May 09, 2013 CELP Restricted Units [Member] Common Units [Member]	Dec. 31, 2013 CELP Restricted Units [Member] Common Units [Member]	Mar. 04, 2013 CELP Restricted Units [Member] Restricted Stock Units (RSUs) [Member]	Mar. 04, 2013 CEI Restricted Shares [Member] Restricted Stock [Member]	May 09, 2013 CEI Restricted Shares [Member] Common Stock [Member]	Dec. 31, 2013 CEI Restricted Shares [Member] Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized									3,470,000				1,785,000
Mandatory Redemption Date 2	Dec. 31, 2013
Non-vested beginning of period		$ 13.31			$ 9.75
Granted		$ 16.19			$ 15.08
Vested*		$ 9.50			$ 7.43
Forfeited		$ 13.52			$ 11.69
Non-vested, end of period		$ 16.11	$ 13.31		$ 12.69	$ 9.75
Non-vested beginning of period		1,003,159			1,329,162
Granted (Units)		625,339			632,912
Vested* (Units)		(396,927)			(445,177)						(57,897)	(60,018)
Forfeited (Units)		(52,648)			(63,864)
Non-vested, end of period		1,178,923	1,003,159		1,453,033	1,329,162
Aggregate intrinsic value, end of period (in thousands)		$ 32,358			$ 51,089
Share based compensation arrangement by share based payment award equity instruments other than options vested in period withheld for payroll taxes		114,831			123,791
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized								8,975,000		9,070,000				4,385,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant								2,464,665
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value		$ 3,771	$ 2,097	$ 5,945	$ 3,307	$ 1,754	$ 5,623				$ 1,000	$ 1,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition		1 year 2 months			1 year 1 month