Significant Accounting Policies - Percentage of Net Service Revenue Earned by Type of Ownership or Relationship with Operating Entity (Detail)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	100.00%	100.00%
Wholly-owned subsidiaries
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	54.20%	56.70%
Equity joint ventures
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	44.10%	41.60%
Other
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	1.70%	1.70%