Collaboration Agreements and Revenues - Transaction Price Related to Consideration Received and Accounts Receivable Allocated to Performance Obligations along with Associated Deferred Revenue (Parenthetical) (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue, net of current ($14,638 and $4,636 to a related party)	$ 151,491	$ 138,474
Deferred Revenue	3,691	2,147
Net unbilled co-development revenue	4,030	0
AstraZeneca Agreements [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred Revenue	142,813	$ 137,338
Net unbilled co-development revenue	3,700
AstraZeneca Agreements [Member] \| U.S./RoW [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue, net of current ($14,638 and $4,636 to a related party)	143,600
Deferred Revenue	147,300
Net unbilled co-development revenue	$ 3,700

Collaboration Agreements and Revenues - Transaction Price Related to Consideration Received and Accounts Receivable Allocated to Performance Obligations along with Associated Deferred Revenue (Parenthetical) (Detail) - USD ($)
$ in Thousands

Mar. 31, 2021

Dec. 31, 2020

Revenue Recognition, Multiple-deliverable Arrangements [Line Items]

Deferred revenue, net of current ($14,638 and $4,636 to a related party)

$ 151,491

$ 138,474

Deferred Revenue

3,691

2,147

Net unbilled co-development revenue

4,030

AstraZeneca Agreements [Member]