Significant Accounting Policies - Percentage of Net Service Revenue Earned by Category of Payor (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Significant Accounting Policies [Line Items]
Percentage of net service revenue	100.00%	100.00%	100.00%	100.00%
Medicare revenue
Significant Accounting Policies [Line Items]
Percentage of net service revenue	75.30%	74.00%	74.90%	74.30%
Medicaid revenue
Significant Accounting Policies [Line Items]
Percentage of net service revenue	1.80%	1.50%	1.70%	1.50%
Other revenue
Significant Accounting Policies [Line Items]
Percentage of net service revenue	22.90%	24.50%	23.40%	24.20%