Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
OG&E Wind Farm Land Lease Agreements [Member]
Long-term Purchase Commitment [Line Items]
Operating Leases, Future Minimum Payments Due, Current	$ 2.0
Operating Leases, Future Minimum Payments, Due in Two Years	2.0
Operating Leases, Future Minimum Payments, Due in Three Years	2.1
Operating Leases, Future Minimum Payments, Due in Four Years	2.1
Operating Leases, Future Minimum Payments, Due in Five Years	2.1
Operating Leases, Future Minimum Payments, Due Thereafter	53.9
Operating Leases, Future Minimum Payments Due	64.2
Railcar Lease [Member]
Long-term Purchase Commitment [Line Items]
Loss Contingency, Range of Possible Loss, Maximum	$ 22.8