Fair Value Measurements Net Profits Plan (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast		5 years
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Profits Plan Liability Noncurrent		$ 7,611
Net Profits Plan Liability Noncurrent		$ 1,162		$ 7,611
Net Profit Plan liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate		10.00%		10.00%
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast		5 years
Period Used for Price Assumptions of Strip Prices for Liabilities		1 year
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Profits Plan Liability Noncurrent		$ 7,611
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	[1]	20,389
Net settlements (1) (2)	[1],[2]	(26,838)
Transfers in (out) of Level 3		0
Net Profits Plan Liability Noncurrent		1,162		$ 7,611
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 Divested Property		$ 21,600	$ 3,800

[1] Net changes in the Company’s Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item in 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 $21.6 million for the nine months ended September 30, 2016, as a result of the divestitures of properties subject to the Net Profits Plan.