Significant Accounting Policies - Percentage of Net Service Revenue Earned by Category of Payor (Detail)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Significant Accounting Policies [Line Items]
Percentage of net service revenue	100.00%	100.00%
Medicare revenue
Significant Accounting Policies [Line Items]
Percentage of net service revenue	74.40%	74.70%
Medicaid revenue
Significant Accounting Policies [Line Items]
Percentage of net service revenue	1.70%	1.40%
Other revenue
Significant Accounting Policies [Line Items]
Percentage of net service revenue	23.90%	23.90%