Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified				1 Months Ended		6 Months Ended
	Jul. 31, 2012	Jul. 31, 2012 Swap [Member]	Jun. 30, 2012 Swap [Member]	Jul. 31, 2012 Interest Rate Swap [Member]	Jul. 31, 2010 Not Designated as Hedging Instrument [Member] Swap [Member]	Jun. 30, 2012 Not Designated as Hedging Instrument [Member] Swap [Member]	Apr. 30, 2012 Not Designated as Hedging Instrument [Member] Swap [Member]	Dec. 31, 2011 Not Designated as Hedging Instrument [Member] Swap [Member]	Jun. 30, 2012 Designated as Hedging Instrument [Member] Interest Rate Cap [Member]	Dec. 31, 2011 Designated as Hedging Instrument [Member] Interest Rate Cap [Member]	Jun. 30, 2012 Designated as Hedging Instrument [Member] Swap [Member]	Jun. 30, 2012 Designated as Hedging Instrument [Member] Swap [Member] Interest Rate Cap [Member]	Dec. 31, 2011 Designated as Hedging Instrument [Member] Swap [Member] Interest Rate Cap [Member]
Derivative [Line Items]
Amount of hedged item						$ 200.0		$ 200.0			$ 35.2
Notional amount fixed spread basis				100		125		150
Interest rate (in hundredths)		2.20%	2.20%			2.46%	2.46%	2.66%
Term of swap (in years)				5
Notional amount fixed spread ratably increases over term of swap					38.0	35.2
Percentage of price depreciation the Company obligated to pay if bonds decline in value (in hundredths)						100.00%
Percentage of price appreciation Citibank obligated to pay if bonds increase in value (in hundredths)						85.00%
Term loan				130
Unsecured Long-term Debt, Noncurrent	150
Fair value of the swap						1.1		1.8
Number of interest rate cap contracts									12
Interest rate cap contracts notional amount									187.8
Tax exempt variable rate debt									202.3
Aggregate carrying value of the interest rate cap contracts									$ 0.1	$ 0.2		$ 5.0	$ 1.4