Derivative Instruments and Hedging Activities (Derivatives By Balance Sheet Location) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative assets - current	$ 167	$ 19,477
Derivative assets - long-term	2,970	36
Derivative liabilities - current	(40,261)	(2,842)
Derivative liabilities - long-term	(16,013)	(23,781)
Total derivatives not designated as hedging instruments	(53,137)	(7,110)
Crude Oil Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative assets - current	167	19,477
Derivative assets - long-term	2,970	36
Derivative liabilities - current	(40,261)	(2,659)
Derivative liabilities - long-term	(16,013)	(23,781)
Deferred Premiums [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities - current	$ 0	$ (183)