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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 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	48.30%	48.20%	49.30%	48.50%
Wholly-owned Subsidiaries [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	49.00%	49.00%	47.90%	48.40%
License Leasing Arrangements [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	1.90%	1.90%	1.90%	2.20%
Management Services [Member]
Health Care Organization, Revenue [Abstract]
Percentage of net service revenue	0.80%	0.90%	0.90%	0.90%