Significant Accounting Policies - Percentage of Net Service Revenue Earned by Type of Ownership or Relationship with Operating Entity (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	100.00%	100.00%	100.00%	100.00%
Equity Joint Ventures [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	48.10%	49.10%	48.90%	48.70%
Wholly-owned Subsidiaries [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	49.30%	48.10%	48.40%	48.50%
License Leasing Arrangements [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	1.80%	1.90%	1.90%	1.90%
Management Services [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	0.80%	0.90%	0.80%	0.90%