Acquisitions (Narrative) (Details) (USD $)	9 Months Ended			9 Months Ended		0 Months Ended	9 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Controlling Interest [Member] Centers	Sep. 30, 2011 Controlling Interest [Member] Centers	Sep. 01, 2011 Acquired Nsc Centers [Member] Centers	Sep. 30, 2012 Acquired Nsc Centers [Member]	Sep. 30, 2011 Acquired Nsc Centers [Member]	Sep. 30, 2012 Prior Year Acquisitions [Member]	Sep. 30, 2012 Prior Year Acquisitions [Member] Working Capital Adjustment Settlement [Member]
Business Acquisition [Line Items]
Number of business acquisitions				3	20	17
Number of business units of acquiree in single transaction						17
Purchase Price Payable	$ 3,100,000		$ 5,236,000
Payments to Acquire Businesses, Net of Cash Acquired	16,097,000	188,500,000							1,829,000	115,000
Additional Contingent Consideration						7,500,000
Purchase Price Placed in Escrow						3,500,000
Business Acquisition Purchase Price Allocation Maximum Amount for Working Capital Adjustments						500,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High						7,500,000
Escrow Release Working Capital							500,000
Goodwill deductible for tax purposes	13,255,000	161,000,000						108,000,000
Other operating expenses in acquisition related costs, primarily attorney fees	$ 128,000	$ 2,657,000