Fair Value Measurements Net Profits Plan (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2015 USD ($) A	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) A	Jun. 30, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability				$ 27,136,000
Net Profits Plan liability		$ 18,326,000		$ 18,326,000
Number of Periods Used for Price Assumptions of Strip Prices of Liabilities | A		5		5
Net Profit Plan liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net Profits Plan liability				$ 27,136,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	[1]			(1,796,000)
Net settlements (1) (2)	[1],[2]			(7,014,000)
Transfers in (out) of Level 3				0
Net Profits Plan liability		$ 18,326,000		$ 18,326,000
Discount Rate Used to Calculate Currently in Payout Liabilities		12.00%		12.00%
Number of Periods Used for Price Assumptions of Strip Prices of Liabilities		5		5
Period Used for Price Assumptions of Strip Prices for Liabilities		1		1
Percent Change in Commodity Prices for Sensitivity Analysis		5.00%		5.00%
Sensitivity Analysis Change in Liability, Due to Change in Commodity Prices		$ 1,794,000		$ 1,794,000
Percent Increase and Decrease in Discount Rate for Sensitivity Analysis		1.00%		1.00%
Sensitivity Analysis Change in Liability Due to Change in Discount Rate		$ 650,000		$ 650,000
Net Profits Plan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Payments Made or Accrued under Profit Sharing Plan Related to Divestiture Proceeds		$ 3,800,000	$ 8,500,000	$ 3,800,000	$ 8,500,000

[1] Net changes in the Company’s Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item of the accompanying statements of operations.

[2] Settlements represent cash payments made or accrued under the Net Profits Plan. The amount in the table includes cash payments made or accrued under the Net Profits Plan of $3.8 million for the six-month period ended June 30, 2015, as a result of the divestitures of properties subject to the Net Profits Plan