Development and Other Agreements - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Nov. 20, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 28, 2018
Development Agreements [Line Items]
Collaborative research and development fee		$ 217.7	$ 0.0	$ 0.0
Collaborative Arrangement \| Verily Life Sciences \| Collaborative Arrangement, Initial Payment
Development Agreements [Line Items]
Initial payment on collaborative agreement	$ 250.0
Issuance of common stock in connection with acquisition, shares	1,840,943
Collaborative research and development fee		$ 217.7
Closing stock price per share					$ 118.28
Collaborative Arrangement \| Verily Life Sciences \| Collaborative Arrangement, Milestone Payments
Development Agreements [Line Items]
Issuance of common stock in connection with acquisition, shares	2,025,036
Additional milestones and incentive payments	$ 280.0
Milestone payments due upon achievement of future development	$ 275.0
Consecutive days used to calculate volume weighted average trading price		15 days