Segment Reporting - Reportable Revenues by Geographic Regions (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Total revenue	$ 75,589	$ 53,369	$ 217,177	$ 133,550
United States
Segment Reporting Information [Line Items]
Total revenue	72,221	50,603	206,736	125,753
Europe
Segment Reporting Information [Line Items]
Total revenue	2,258	1,974	7,210	5,512
Rest of World
Segment Reporting Information [Line Items]
Total revenue	1,110	792	3,231	2,285
Testing services revenue
Segment Reporting Information [Line Items]
Total revenue	66,464	45,529	190,635	113,264
Testing services revenue | United States
Segment Reporting Information [Line Items]
Total revenue	66,096	45,439	189,956	112,976
Testing services revenue | Rest of World
Segment Reporting Information [Line Items]
Total revenue	368	90	679	288
Product revenue
Segment Reporting Information [Line Items]
Total revenue	6,521	5,383	19,160	13,369
Product revenue | United States
Segment Reporting Information [Line Items]
Total revenue	3,595	2,755	9,555	6,032
Product revenue | Europe
Segment Reporting Information [Line Items]
Total revenue	2,227	1,950	7,138	5,448
Product revenue | Rest of World
Segment Reporting Information [Line Items]
Total revenue	699	678	2,467	1,889
Digital and other revenue
Segment Reporting Information [Line Items]
Total revenue	2,604	2,457	7,382	6,917
Digital and other revenue | United States
Segment Reporting Information [Line Items]
Total revenue	2,530	2,409	7,225	6,745
Digital and other revenue | Europe
Segment Reporting Information [Line Items]
Total revenue	31	24	72	64
Digital and other revenue | Rest of World
Segment Reporting Information [Line Items]
Total revenue	$ 43	$ 24	$ 85	$ 108