Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 Y Centers	Dec. 31, 2010	Dec. 31, 2009
Intangible Assets
Finite-Lived Intangible Assets, Useful Life, Minimum	5
Finite-Lived Intangible Assets, Useful Life, Maximum	10
Operating Expenses [Abstract]
Bad debt expense included in other operating expenses	$ 18,449,000	$ 16,945,000	$ 16,781,000
Other Long Term Liabilities
Deferred Rent Credit, Noncurrent	10,255,000	8,555,000
Liability for Uncertain Tax Positions, Noncurrent	8,356,000	8,434,000
Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities	5,236,000	3,895,000
Off-market Lease, Unfavorable	4,084,000	2,581,000
Interest Rate Derivative Liabilities, at Fair Value	0	902,000
Other long-term liabilities	200,000	37,000
Prepaid Expense and Other Current Assets
Short-term Investments	6,516,000	6,450,000
Other Prepaid Expense, Current	5,674,000	4,386,000
Prepaid Insurance	4,185,000	3,402,000
Accounts and Other Receivables, Net, Current	4,394,000	2,063,000
Income Taxes Receivable, Current	0	1,555,000
Other Assets, Current	1,106,000	804,000
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	3
Ownership Interest In Unconsolidated Minority Owned Partnerships	20.00%
Revenue Recognition
Percentage of revenues from governmental healthcare programs	29.00%	31.00%	33.00%
Share-based Compensation [Abstract]
Excess Tax Benefit from Share-based Compensation, Financing Activities	977,000	200,000	32,000
Use Of Estimates [Abstract]
Allowances for contractual adjustments	136,265,000	118,503,000
Allowances for accounts receivable	$ 18,844,000	$ 13,070,000
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life, Minimum	20
Property, Plant and Equipment, Useful Life, Maximum	40
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life, Minimum	3
Property, Plant and Equipment, Useful Life, Maximum	10
Consolidated [Member]
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	1
Nonconsolidated [Member]
Ownership Interests [Line Items]
Number Of Centers Owned Less Than 51 Percent	2
Number Of Centers Owned Greater Than 51 Percent	0