Commitments and Contingencies - Income Tax Examination (Details) (Indiana Income Tax [Member], USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Dec. 31, 2011
Indiana Income Tax [Member]
Income Tax Examination [Line Items]
Proposed penalties and interest expense	$ 2.3
Proposed adjustment excluding interest and penalties	$ 7.3
Income Tax Exmination Tax Dispute, Additional Fact Review Period		60 days