Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) (USD $)	Mar. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	$ 36,000,000
Natural gas financial swaps	60,000,000
Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	5.99
Natural gas financial swaps	2.85
Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	49.70
Natural gas financial swaps	4.83
Weighted average [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Electricity financial swaps	38.33
Natural gas financial swaps	$ 3.71