The Company, Business Activities and Basis of Presentation - Composition of Net Revenues Recognized Disaggregated by Source (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Disaggregation Of Revenue [Line Items]
Total net revenues		$ 19,945	$ 17,756
Commercial Revenues [Member] | Commercial Revenues
Disaggregation Of Revenue [Line Items]
Total net revenues		19,907	17,655
Commercial Revenues [Member] | Contracted Payers [Member]
Disaggregation Of Revenue [Line Items]
Total net revenues	[1]	12,645	11,341
Commercial Revenues [Member] | Non-Contracted Payers [Member]
Disaggregation Of Revenue [Line Items]
Total net revenues		7,262	6,314
Development Services Revenues [Member]
Disaggregation Of Revenue [Line Items]
Total net revenues		$ 38	39
Kits and Specimen Collection Tubes (SCTs)
Disaggregation Of Revenue [Line Items]
Total net revenues			$ 62

[1] Includes Medicare, Medicare Advantage and CARES Act as reimbursement amounts are fixed.