Derivatives (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Caps
Open interest rate contracts
Year Entered	2012
Year of Maturity	2013
Initial Notional Amount (in millions)	$ 80.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Swap
Open interest rate contracts
Year Entered	2006
Year of Maturity	2016
Initial Notional Amount (in millions)	4.0
Hedged Item	Interest rate component of an operating lease - not accounted for as a hedge
Interest Rate	5.20%
Swap
Open interest rate contracts
Year Entered	2006
Year of Maturity	2016
Initial Notional Amount (in millions)	14.0
Hedged Item	Interest rate component of debt - accounted for as cash flow hedge
Interest Rate	6.00%
Swap
Open interest rate contracts
Year Entered	2012
Year of Maturity	2023
Initial Notional Amount (in millions)	23.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Interest Rate	4.40%
Caps
Open interest rate contracts
Year Entered	2012
Year of Maturity	2014
Initial Notional Amount (in millions)	40.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Cap
Open interest rate contracts
Year Entered	2012
Year of Maturity	2015
Initial Notional Amount (in millions)	10.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Interest Rate	0.90%
Cap
Open interest rate contracts
Year Entered	2012
Year of Maturity	2016
Initial Notional Amount (in millions)	$ 10.0
Hedged Item	Interest rate component of debt - not accounted for as a hedge
Interest Rate	1.50%
Minimum | Caps
Open interest rate contracts
Interest Rate	0.60%
Minimum | Caps
Open interest rate contracts
Interest Rate	0.80%
Maximum | Caps
Open interest rate contracts
Interest Rate	1.70%
Maximum | Caps
Open interest rate contracts
Interest Rate	1.40%