Significant Accounting Policies - Percentage of Net Service Revenue Earned by Type of Ownership or Relationship with Operating Entity (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	100.00%	100.00%	100.00%	100.00%
Wholly-owned subsidiaries
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	53.30%	57.00%	53.50%	56.90%
Equity joint ventures
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	45.10%	41.30%	44.80%	41.40%
Other
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	1.60%	1.70%	1.70%	1.70%