Contingent Liabilities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Loss Contingencies [Line Items]
Aggregate amount of counterparty obligations	$ 15.1		$ 15.1		$ 18.4
VSC counterparty contingency expense	3.1	0.3	3.3	0.8
Reserve	2.2		2.2		1.4
Provision for loss reimbursement on sold loans	0.10	0.20	0.20	0.70	1.20	0.50	0.20	0.06
Pending Litigation [Member]
Loss Contingencies [Line Items]
Maximum range of reasonably possible loss	$ 0.4		$ 0.4
Accounts Receivables Due to Mepco [Member]
Loss Contingencies [Line Items]
Installment payments period for service contract, minimum	12 months
Installment payments period for service contract, maximum	24 months