Long-Term Debt -Interest Rate Caps (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Interest Rate Cap, fair value	$ 0.2	$ 0.1
Cap agreement effective January 14, 2013-2015 [Member]
Derivative [Line Items]
Interest Rate Cap, number of agreements	10
Interest Rate Cap, notional amount	1,150.0
Interest Rate Cap Purchased During 2011 [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	500.0
Interest Rate Cap, cap rate	3.50%
Interest Rate Cap Purchased During 2012 [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments	650.0
Interest Rate Cap, cap rate	1.50%
Senior Notes, due 2015 [Member]
Derivative [Line Items]
Debt, short-term and long-term	$ 0	$ 0	$ 129.0