Derivatives (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated OCI gain, net of tax	$ 9,912,000	[1]	$ 37,323,000	[1]
Period over which gain included in AOCI will be transferred to earnings, months	12
Expected earnings transfer	8,300,000
Expected derivative maturity date	Dec. 31, 2013
Commodity Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated OCI gain, net of tax	$ 9,912,000	[1]	$ 37,323,000	[1]

[1] Net of taxes.