Commitments, Guarantees and Contingencies - Leasing Agreements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Leasing Agreements [Line Items]
Operating Leases, Future Minimum Payments, Due in Current Year	$ 11.5
Operating Leases, Future Minimum Payments, Due in Year Two	11.7
Operating Leases, Future Minimum Payments, Due in Year Three	11.4
Operating Leases, Future Minimum Payments, Due in Year Four	9.3
Operating Leases, Future Minimum Payments, Due in Year Five	8.5
Operating Leases, Future Minimum Payments, Due Thereafter	35.0
BNI Coal Dragline Lease [Member]
Leasing Agreements [Line Items]
Termination Fee	3.0
Operating Leases, Future Minimum Payments, Due in Current Year	$ 2.8