Derivative Instruments and Hedging Activities Notional Contracts by Derivative Type (Details)	Dec. 31, 2013 MMBTU
Natural Gas [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	38,400,000
WTI crude oil - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	18,797,500
Ultra-low sulfur diesel - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	15,512,500
Sub octane gasoline - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	3,285,000
Commodity price swap (natural gas) - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	6,387,500
Commodity Price Swap Natural Gas Long [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	38,400,000
Commodity Price Swap Natural Gas Short [Member] [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	38,400,000
NYMEX WTI Short [Member]
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	1,946,000
Commodity price swap (gasoline) - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	300,000
Commodity Butane [Member]
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	300,000
Maturing in Next Twelve Months [Member] | Natural Gas [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Next Twelve Months [Member] | WTI crude oil - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	16,242,500
Maturing in Next Twelve Months [Member] | Ultra-low sulfur diesel - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	12,957,500
Maturing in Next Twelve Months [Member] | Sub octane gasoline - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	3,285,000
Maturing in Next Twelve Months [Member] | Commodity price swap (natural gas) - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	6,387,500
Maturing in Next Twelve Months [Member] | Commodity Price Swap Natural Gas Long [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Next Twelve Months [Member] | Commodity Price Swap Natural Gas Short [Member] [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Next Twelve Months [Member] | NYMEX WTI Short [Member]
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	1,946,000
Maturing in Next Twelve Months [Member] | Commodity price swap (gasoline) - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	300,000
Maturing in Next Twelve Months [Member] | Commodity Butane [Member]
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	300,000
Maturing in Year Two [Member] | Natural Gas [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Two [Member] | WTI crude oil - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	2,555,000
Maturing in Year Two [Member] | Ultra-low sulfur diesel - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	2,555,000
Maturing in Year Two [Member] | Sub octane gasoline - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Two [Member] | Commodity Price Swap Natural Gas Long [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Two [Member] | Commodity Price Swap Natural Gas Short [Member] [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Three [Member] | Natural Gas [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Three [Member] | WTI crude oil - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Three [Member] | Ultra-low sulfur diesel - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Three [Member] | Sub octane gasoline - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Three [Member] | Commodity Price Swap Natural Gas Long [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Three [Member] | Commodity Price Swap Natural Gas Short [Member] [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Four [Member] | Natural Gas [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Four [Member] | WTI crude oil - long
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Four [Member] | Ultra-low sulfur diesel - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Four [Member] | Sub octane gasoline - short
economic hedges by derivative type [Line Items]
Notional contract volumes related to swap contracts serving as hedges	0
Maturing in Year Four [Member] | Commodity Price Swap Natural Gas Long [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000
Maturing in Year Four [Member] | Commodity Price Swap Natural Gas Short [Member] [Member]
economic hedges by derivative type [Line Items]
Portion Of Future Gas Production Being Hedged	9,600,000