Revenue - Summary of Total Revenue by Type of Service (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue, Major Customer [Line Items]
Revenues	$ 169,557	$ 117,602	$ 468,255	$ 325,550
Screening Services [Member]
Revenue, Major Customer [Line Items]
Revenues	168,372	116,313	463,763	320,596
Other Services [Member]
Revenue, Major Customer [Line Items]
Revenues	$ 1,185	$ 1,289	$ 4,492	$ 4,954