Acquisitions (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended					0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Noncontrolling Interest Number Of Centers [Member] Centers	Sep. 30, 2013 Controlling Interest [Member] Centers	Sep. 30, 2012 Controlling Interest [Member] Centers	Sep. 01, 2011 Acquired Nsc Centers [Member] Centers	Sep. 30, 2013 Acquired Nsc Centers [Member]	Dec. 31, 2012 Acquired Nsc Centers [Member]	Sep. 30, 2013 Current Year Acquisitions [Member]
Business Acquisition [Line Items]
Equity Method Investments	$ 16,970,000		$ 16,970,000		$ 11,274,000									$ 5,201,000
Gain (loss) on deconsolidation	0	0	2,237,000	0
Estimated Probability Of Fair Value Variables Range						5.00%	30.00%
Number of business acquisitions								1	4	3	17
Payments to Acquire Businesses, Net of Cash Acquired			59,455,000	16,097,000
Purchase Price Payable Commitment													2,744,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High											7,500,000
Contingent Purchase Price Obligation, Settlement Amount	2,744,000		2,744,000									2,744,000
Goodwill deductible for tax purposes	56,173,000	13,255,000	56,173,000	13,255,000
Other operating expenses in acquisition related costs, primarily attorney fees			$ 285,000	$ 128,000