Acquisitions and Disposals (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) physician_practice center	Sep. 30, 2015 USD ($) physician_practice center	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Acquisitions and related expenses, net			$ 351,736	$ 233,490
Net change in fair value of contingent consideration	$ 0	$ 1,928	(2,598)	8,338
Transaction costs	16,906	$ 2,107	$ 23,431	$ 5,560
Ambulatory Services [Member]
Business Acquisition [Line Items]
Number of business acquisitions | center			7	5
Acquisitions and related expenses, net			$ 39,400	$ 112,900
Ambulatory Services [Member] | Disposal Group, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Number of center disposals | center			3	0
Net gain from disposals			$ 7,400
Physician Services [Member]
Business Acquisition [Line Items]
Net change in fair value of contingent consideration			$ (2,600)
Physician Services [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Number of business acquisitions | physician_practice			8	6
Cash paid to acquire business			$ 312,400	$ 120,600
Deferred Consideration			$ 15,400
Deferred consideration period			2 years
Payment of deferred purchase price			$ 4,000
Accrued liability, contingent consideration	1,000		1,000		$ 5,500
Cash payment for previous acquisition			1,900
Contingent consideration arrangements, high	$ 1,000		$ 1,000