Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities (Derivatives Designated as Hedging Instruments/ Derivatives Not Designated as Hedging Instruments) (Details)

v2.4.0.6
Derivative Instruments and Hedging Activities (Derivatives Designated as Hedging Instruments/ Derivatives Not Designated as Hedging Instruments) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]      
Unrealized loss, net $ 1,683 $ 0 $ 0
Total gain on derivative instruments, net 1,717 0 0
Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Gain (Loss) Reclassified from OCI into Income 1,420 (375) 632
Amount of Gain Recognized in Income 0 0 0
Commodity Contract [Member] | Not Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Total gain on derivative instruments, net 1,717 0 0
Commodity Contract [Member] | Natural gas [Member] | Not Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Realized gain, net 34 0 0
Unrealized loss, net (241) 0 0
Total gain on derivative instruments, net (207) 0 0
Commodity Contract [Member] | Crude Oil [Member] | Not Designated as Hedging Instrument [Member]
     
Derivative Instruments, Gain (Loss) [Line Items]      
Realized gain, net 0 0 0
Unrealized loss, net 1,924 0 0
Total gain on derivative instruments, net $ 1,924 $ 0 $ 0