Debt (Schedule Of Debt) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Debt Instrument [Line Items]
Senior Notes	$ 600,000	$ 600,000
Unamortized discount	(5,163)	(5,464)
Long-term Debt	833,128	729,300
Current maturities of Huntington Facility due June 30, 2013	16,650	0	0
Long-term Debt, Excluding Current Maturities, Total	816,478	729,300
Senior Secured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility amount outstanding	130,000	47,000
U.K. Huntington Field Development Project Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility amount outstanding	37,000	17,813
Current maturities of Huntington Facility due June 30, 2013	16,650
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized discount	(2,459)	(3,799)
Convertible Senior Notes	$ 73,750	$ 73,750