Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 Centers	Dec. 31, 2012	Dec. 31, 2011
Accounts Receivable, Net [Abstract]
Allowances for contractual adjustments	$ 289,937,000	$ 216,363,000
Allowances for accounts receivable	27,862,000	22,379,000
Income Taxes
Open Tax Year	2010
Operating Expenses [Abstract]
Bad debt expense included in other operating expenses	21,947,000	20,005,000	18,230,000
Other Long Term Liabilities
Deferred Rent Credit, Noncurrent	14,637,000	12,134,000
Liability for Uncertain Tax Positions, Noncurrent	6,888,000	10,113,000
Off-market Lease, Unfavorable	3,034,000	3,559,000
Other long-term liabilities	944,000	166,000
Prepaid Expense and Other Current Assets
Short-term Investments	13,313,000	8,804,000
Other Prepaid Expense, Current	7,099,000	6,462,000
Prepaid Insurance	5,631,000	4,963,000
Accounts and Other Receivables, Net, Current	6,126,000	5,926,000
Other Assets, Current	1,433,000	1,382,000
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	6
Ownership Interest In Unconsolidated Minority Owned Partnerships	20.00%
Revenue Recognition
Percentage of revenues from governmental healthcare programs	25.00%	27.00%	29.00%
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years 8 months 12 days
Share-based Compensation [Abstract]
Excess Tax Benefit from Share-based Compensation, Financing Activities	$ 7,247,000	$ 1,784,000	$ 977,000
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Maximum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Maximum [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Minimum [Member] | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum [Member] | Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Consolidated [Member]
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	3
Nonconsolidated [Member]
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	3
Number Of Centers Owned Greater Than 51 Percent	0