Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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The aggregate amount of receivables to be collected from related parties where one party can exercise control or significant influence over another party; including affiliates, owners or officers and their immediate families, pension trusts, and so forth, at the financial statement date. which are usually due within one year (or one business cycle).

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Carrying amount as of the balance sheet date of obligations due all related parties.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of selling, general and administrative expenses resulting from transactions, excluding transactions that are eliminated in consolidated or combined financial statements, with related party.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Related Party Transactions - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Collaboration revenue - related party	$ 23,015,000	$ 13,015,000	$ 29,044,000	$ 18,730,000
Flagship Ventures Management INC [Member] \| Services Agreement [Member]
Related Party Transaction [Line Items]
Payments under agreements with related party	0	0	0	17,000
Due to related party	0		0		$ 0
Nestlé Health Science [Member]
Related Party Transaction [Line Items]
Payments under agreements with related party	0		0
Collaboration revenue - related party	23,015,000	$ 13,015,000	29,044,000	$ 18,730,000
Deferred revenue	99,770,000		99,770,000
Due from related party for the reimbursement of development costs	$ 297,000		$ 297,000