Collaborative arrangement term of agreement.

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Collaborative arrangement transaction price.

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Cost reimbursement.

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Deferred revenue recognition period.

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Gross revenue.

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Percentage of revenue related to worldwide development cost.

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Remaining deferred revenue.

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Upfront non refundable fees.

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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, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

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Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Amount of billed or unbilled claims or other similar items subject to uncertainty concerning their determination or ultimate realization under long-term contracts.

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Amount of revenue earned from products sold or services provided under the terms of a contract, including, but not limited to, government contracts and construction contracts, classified as other.

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Amount of deferred revenue recognized for transactions arising during the current reporting period. Deferred revenue is a liability as of the balance sheet date 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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Amount of revenue recognized that was previously reported as deferred or unearned revenue.

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Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

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Year in which remaining performance obligation is expected to be recognized, in CCYY format.

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Collaboration revenue - Additional Information (Detail) - USD ($)			3 Months Ended
	Jun. 03, 2015	Mar. 19, 2013	Mar. 31, 2018	Mar. 31, 2017	Mar. 28, 2018	Sep. 28, 2017	Feb. 16, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue			$ 15,608,000	$ 6,832,000
Contract assets			0
Deferred revenue balance recognized as gross revenues			13,966,000
Celgene Corporation [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Term of collaboration agreement		3 years
Celgene Corporation [Member] \| Amended Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			10,000,000
Collaboration agreement, transaction price			176,200,000
Up-front non-refundable fees			$ 100,000,000
Deferred revenue recognition period			3 years
Percentage of revenue related to worldwide development cost			67.50%
Celgene Corporation [Member] \| Amended Collaborative Arrangement [Member] \| Research and Development Services [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price			$ 34,800,000
Deferred revenue recognized			2,200,000	1,500,000
Remaining deferred revenue			100,000
Celgene Corporation [Member] \| bb2121 License Agreement [Member] \| First Product Candidates [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event							$ 10,000,000
Celgene Corporation [Member] \| bb2121 Co-Development, Co-Promote and Profit Share Agreement [Member] \| Development Milestone Payments [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event					$ 70,000,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			$ 15,000,000			$ 15,000,000
Deferred revenue recognition period			2 years
Deferred revenue recognized			$ 41,700,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member] \| Co-Develop and Co-Promote Options not Exercise [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event						$ 10,000,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member] \| Clinical Milestones Payments [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			10,000,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member] \| Regulatory Milestones Payments [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			117,000,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member] \| Commercial Milestones Payments [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			78,000,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member] \| Research and Development Services [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price			5,400,000
Deferred revenue recognized			700,000	0
Remaining deferred revenue			4,300
Remaining performance obligation revenue			4,000,000
Celgene Corporation [Member] \| bb21217 License Agreement [Member] \| License and Manufacturing Services [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue recognized			0	0
Remaining deferred revenue			9,800
Remaining performance obligation revenue			$ 36,200,000
Remaining performance obligation expected to be recognize as revenue, year			2019
Celgene Corporation [Member] \| bb21217 License Agreement, Co-promotion and Development [Member] \| Development Milestone Payments [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			$ 70,000,000
Celgene Corporation [Member] \| bb2121 License and Manufacturing Services [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, transaction price			141,400,000
Deferred revenue recognized			3,900,000
Collaboration revenue			8,800,000
Gross revenue			11,800,000
Cost reimbursement			7,900,000
Celgene Corporation [Member] \| bb2121 License and Manufacturing Services [Member] \| ASC 605 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration revenue				$ 4,900,000
Celgene Corporation [Member] \| bb2121 License and Manufacturing Services [Member] \| License and Manufacturing Services [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Remaining deferred revenue			48,600,000
Remaining performance obligation revenue			$ 90,700,000
Remaining performance obligation expected to be recognize as revenue, year			2021
Up-front Payment Arrangement [Member] \| Celgene Corporation [Member] \| Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, cash payment received		$ 75,000,000
Up-front Payment Arrangement [Member] \| Celgene Corporation [Member] \| Amended Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, cash payment received	$ 25,000,000