Summary of Significant Accounting Policies - Percentage of Net Service Revenue Earned by Type of Ownership or relationship with Operating Entity (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Health Care organization, Revenue [Abstract]
Percentage of Net Service Revenue	100.00%	100.00%	100.00%
Wholly-owned Subsidiaries [Member]
Health Care organization, Revenue [Abstract]
Percentage of Net Service Revenue	57.20%	55.20%	53.50%
Equity Joint Ventures [Member]
Health Care organization, Revenue [Abstract]
Percentage of Net Service Revenue	41.20%	42.90%	43.90%
Other Arrangements [Member]
Health Care organization, Revenue [Abstract]
Percentage of Net Service Revenue	1.60%	1.90%	2.60%