Percentage of Net Revenue and Total Accounts Receivable (Detail)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Payor F [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage		14.10%		[1]
Sales Revenue, Net | Payor A [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage		14.60%	14.10%
Sales Revenue, Net | Payor B [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage		18.70%	18.10%
Sales Revenue, Net | Payor C [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage	[1]		11.10%
Sales Revenue, Net | Payor D [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage		14.10%	11.30%
Accounts Receivable | Payor D [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage		34.10%	23.80%
Accounts Receivable | Payor E [Member]
Accounts Receivable And Net Revenue [Line Items]
Concentration Risk, Percentage		42.20%	30.50%

[1] Less than 10% of total net revenues