Accounts Receivable and Accounts Payable and Accrued Expenses Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable
Accounts Receivable, Net, Current	$ 254,805	$ 210,368
Accrued oil, gas, and NGL sales
Accounts, Notes, Loans and Financing Receivable
Accounts Receivable, Net, Current	160,568	149,384
Due From Joint Interest Owner
Accounts, Notes, Loans and Financing Receivable
Accounts Receivable, Net, Current	42,740	30,784
Mitsui Receivable [Member]
Accounts, Notes, Loans and Financing Receivable
Accounts Receivable, Net, Current	19,931	0
Taxes Receivable
Accounts, Notes, Loans and Financing Receivable
Accounts Receivable, Net, Current	17,237	14,979
Other Receivables
Accounts, Notes, Loans and Financing Receivable
Accounts Receivable, Net, Current	$ 14,329	$ 15,221