Acquisitions and Disposals (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) physician_practice center	Jun. 30, 2015 USD ($) physician_practice center	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Acquisitions and related expenses, net			$ 281,113	$ 196,032
Net change in fair value of contingent consideration	$ (2,598)	$ 6,410	(2,598)	6,410
Transaction costs	5,135	$ 1,982	$ 6,525	$ 3,453
Ambulatory Services [Member]
Business Acquisition [Line Items]
Number of business acquisitions | center			4	4
Acquisitions and related expenses, net			$ 25,700	$ 95,400
Ambulatory Services [Member] | Disposal Group, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Number of center disposals | center			2	0
Net gain from disposals			$ 3,300
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			6	4
Cash paid to acquire business			$ 255,400	$ 100,700
Deferred Consideration			$ 15,400
Deferred consideration period			2 years
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
Other Accrued Liabilities [Member] | Physician Services [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Deferred Consideration			9,700
Other Long-term Liabilities [Member] | Physician Services [Member] | Series of Individually Immaterial Business Acquisitions [Member]
Business Acquisition [Line Items]
Deferred Consideration			$ 5,700