Collaboration Revenue - Additional Information (Detail) - USD ($)				3 Months Ended		12 Months Ended
	Jul. 21, 2021	Jul. 01, 2021	Jan. 31, 2016	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2018	Feb. 29, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration (profit) loss sharing - related party				$ 976,000	$ 0
Change in collaboration revenue-related party				(1,493,000)	4,648,000
Upfront collaboration/license fee			$ 120,000,000
Collaboration revenue - related party				1,493,000	4,648,000
2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration product, percentage of commercial profit		50.00%
Collaborative arrangement, sharing of pre-launch costs, percentage		50.00%
Nestle Health Science [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment				97,003,000		$ 97,728,000						$ 120,000,000
Maximum development milestone payments to be received				285,000,000
Maximum regulatory payments to be received				375,000,000
Maximum amount to be received on achievement of certain commercial milestones				1,125,000,000
Proceeds on achievement of development milestone							$ 10,000,000	$ 40,000,000	$ 20,000,000	$ 10,000,000
Transaction price allocated to remaining performance obligations				200,000,000
Collaboration revenue - related party				725,000	$ 4,648,000
Deferred revenue				102,324,000		103,817,000
Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration product, percentage of commercial profit		50.00%
Upfront payment received	$ 175,000,000
Maximum Amount To Be Received On Achievement Of Regulatory and Sales Milestones		$ 360,000,000
Maximum amount to be received on achievement of sales milestones		225,000,000
Collaboration (profit) loss sharing - related party				976,000
Maximum regulatory payments to be received		$ 135,000,000
Transaction price allocated to remaining performance obligations	$ 139,500,000
Termination notice period	60 days
Nestle Health Science [Member] | Phase 2 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable			20,000,000
Nestle Health Science [Member] | Phase 3 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable			$ 20,000,000
Nestle Health Science [Member] | Phase 2b [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront collaboration milestone payments receivable											$ 40,000,000
Proceeds on achievement of development milestone								$ 40,000,000
License [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party						$ 131,343,000
Service [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue - related party				768,000
Topic 808 [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement	$ 35,500,000
Topic 808 [Member] | Total Liabilities [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement	$ 35,500,000
Topic 808 [Member] | Other Noncurrent Liabilities [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement				2,981,000
Topic 808 [Member] | Accrued Expenses and Other Current Liabilities [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price allocated under collaborative arrangement				29,809,000
Research and Development Expense [Member] | Topic 808 [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cost associated with pre-launch activities				1,635,000
General and Administrative Expense [Member] | Topic 808 [Member] | Nestle Health Science [Member] | 2021 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cost associated with pre-launch activities				$ 2,438,000