Derivative Instruments Derivative Instruments (Commodity Derivatives) (Details) - 2016 [Member] - Natural gas basis differential commodity contract [Member]	Dec. 31, 2015 mmbls $ / mmbls	[2]
NWPL Rockies basis swaps: (2)
Derivative [Line Items]
Hedged volume (MMMBtu) | mmbls	11,712	[1]
Hedged differential ($/MMBtu) | $ / mmbls	(0.34)	[1]
SoCal basis swaps: (3)
Derivative [Line Items]
Hedged volume (MMMBtu) | mmbls	32,940	[3]
Hedged differential ($/MMBtu) | $ / mmbls	(0.03)	[3]

[1] For positions which hedge exposure to differentials in producing areas, the Company receives the NYMEX Henry Hub natural gas price plus the respective spread and pays the specified index price. Cash settlements are made on a net basis.

[2] Settle on the respective pricing index to hedge basis differential to the NYMEX Henry Hub natural gas price.

[3] For positions which hedge exposure to differentials in consuming areas, the Company pays the NYMEX Henry Hub natural gas price plus the respective spread and receives the specified index price. Cash settlements are made on a net basis.