Derivative Financial Instruments (Derivatives and Hedging-Designated) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
NYMEX Commodity Contracts [Member] | Energy Commodity Derivatives Contracts [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives	$ 2,209
Liability Derivatives	107
NYMEX Commodity Contracts [Member] | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives	10,962	4,920
NYMEX Commodity Contracts [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member]
Asset Derivatives
Interest Rate Swap Agreements [Member] | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument [Member]
Liability Derivatives
Interest Rate Swap Agreements [Member] | Other Current Assets [Member] | Designated as Hedging Instrument [Member]
Asset Derivatives	2,678
Interest Rate Swap Agreements [Member] | Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member]
Asset Derivatives	1,849
Interest Rate Swap Agreements [Member] | Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Liability Derivatives
Designated as Hedging Instrument [Member]
Asset Derivatives	6,736
Liability Derivatives	11,069
NYMEX Commodity Contracts [Member]
Liability Derivatives	$ 18,400