Fair Value Measurements Fair Value Measurements (Nonrecurring Fair Value Measurements) (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) $ / Mcf $ / bbl	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory Write-down	$ 3,000				$ 9,000
Impairment of oil and gas properties	$ 0		$ 0		$ 138,000	$ 0
Management oil price outlook | $ / bbl		65.02
Management gas price outlook | $ / Mcf		3.83
West Panhandle [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of oil and gas properties		$ 138,000
Discontinued Operations [Member] | Pioneer Alaska [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of oil and gas properties				$ 97,000
Discontinued Operations [Member] | Barnett Shale Field [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of oil and gas properties			$ 114,000			$ 128,000