Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Centers	Dec. 31, 2011	Dec. 31, 2010
Income Taxes
Open Tax Year	2009
Operating Expenses [Abstract]
Bad debt expense included in other operating expenses	$ 20,073,000	$ 18,449,000	$ 16,945,000
Other Long Term Liabilities
Deferred Rent Credit, Noncurrent	12,134,000	10,255,000
Liability for Uncertain Tax Positions, Noncurrent	10,113,000	8,356,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities		5,236,000
Off-market Lease, Unfavorable	3,559,000	4,084,000
Other long-term liabilities	166,000	200,000
Prepaid Expense and Other Current Assets
Short-term Investments	8,804,000	6,516,000
Other Prepaid Expense, Current	6,462,000	5,674,000
Prepaid Insurance	4,963,000	4,185,000
Accounts and Other Receivables, Net, Current	5,926,000	4,394,000
Other Assets, Current	1,382,000	1,106,000
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	5
Ownership Interest In Unconsolidated Minority Owned Partnerships	20.00%
Revenue Recognition
Percentage of revenues from governmental healthcare programs	27.00%	29.00%	31.00%
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years 8 months 18 days
Share-based Compensation [Abstract]
Excess Tax Benefit from Share-based Compensation, Financing Activities	1,784,000	977,000	200,000
Use Of Estimates [Abstract]
Allowances for contractual adjustments	216,363,000	136,265,000
Allowances for accounts receivable	$ 22,379,000	$ 18,844,000
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	2
Number Of Centers Owned Greater Than 51 Percent	0