Acquisitions - Additional Information (Detail) - Counsyl Inc [Member] $ / shares in Units, $ in Millions		3 Months Ended	18 Months Ended
	Jul. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)
Business Acquisition [Line Items]
Business acquisition consideration	$ 405.9
Acquisition costs	6.8
Goodwill, working capital adjustment reduction		$ (1.1)	$ (1.1)
Acquired intangible assets	290.0
Developed Screening Processes [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 290.0
Intangible assets estimated useful lives	12 years
Developed Screening Processes [Member] | Measurement Input, Discount Rate [Member]
Business Acquisition [Line Items]
Estimated net cash flows, discount rate	12.5
Agreement and Plan of Merger [Member]
Business Acquisition [Line Items]
Effective date of business acquisition	Jul. 31, 2018
Business acquisition consideration	$ 405.9
Cash payment on business acquisition	278.5
Amount of cash consideration deposited in escrow account	$ 5.0
Agreement and Plan of Merger [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Business acquisition, shares issued | shares	2,994,251
Business acquisition, shares issued, value	$ 127.4
Business acquisition, per share market closing price | $ / shares	$ 42.53