Fair Value Measurements (Details) (USD $) In Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2011		Dec. 31, 2010
Swap Four [Member] | Fair Value, Inputs, Level 1 [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Assets			$ 0
Swap One [Member] | Fair Value, Inputs, Level 1 [Member] | Accrued expenses and other current [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Liabilities			0
Fair Value, Inputs, Level 1 [Member] | Restricted marketable securities [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	0		0
Fair Value, Inputs, Level 1 [Member] | Restricted marketable securities [Member] | Other long term assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	0		0
Swap Four [Member] | Fair Value, Inputs, Level 2 [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Assets			1.2
Swap One [Member] | Fair Value, Inputs, Level 2 [Member] | Accrued expenses and other current [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Liabilities			(12.1)
Fair Value, Inputs, Level 2 [Member] | Restricted marketable securities [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	22.0		18.2
Fair Value, Inputs, Level 2 [Member] | Restricted marketable securities [Member] | Other long term assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	23.7		19.3
Swap Four [Member] | Fair Value, Inputs, Level 3 [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Assets			0
Swap One [Member] | Fair Value, Inputs, Level 3 [Member] | Accrued expenses and other current [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Liabilities			0
Fair Value, Inputs, Level 3 [Member] | Restricted marketable securities [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	0		0
Fair Value, Inputs, Level 3 [Member] | Restricted marketable securities [Member] | Other long term assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	0		0
Restricted marketable securities [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	22.0		18.2
Fair Value, Assets Measured on Recurring Basis, Investments, Valuation Techniques	M	[1]	M	[1]
Restricted marketable securities [Member] | Other long term assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair Value, Measured on Recurring Basis, Investments	23.7		19.3
Fair Value, Assets Measured on Recurring Basis, Investments, Valuation Techniques	M	[1]	M	[1]
Swap One [Member] | Accrued expenses and other current [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Liabilities			(12.1)
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities, Valuation Techniques			I	[1]
Swap Four [Member] | Other current assets [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Fair market value of swap, Assets			$ 1.2
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets, Valuation Techniques			I	[1]

[1] The three valuation techniques are: market approach (M), cost approach (C), and income approach (I).