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Amount of revenue recognized arising from contract liability from change in timeframe for performance obligation to be satisfied.

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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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The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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License and royalty revenue - Additional Information (Detail)			1 Months Ended	3 Months Ended									12 Months Ended
	Apr. 28, 2017 USD ($) performance_obligation	Apr. 26, 2017 USD ($) performance_obligation	Aug. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
License And Royalty Revenue [Line Items]
Revenue				$ 9,997,000	$ 8,910,000	$ 13,296,000	$ 12,471,000	$ 19,243,000	$ 11,528,000	$ 7,851,000	$ 15,957,000		$ 44,674,000	$ 54,579,000	$ 35,427,000
Cost of license and royalty revenue													2,978,000	885,000	1,527,000
License and royalty revenue
License And Royalty Revenue [Line Items]
Revenue													8,205,000	2,226,000	$ 13,220,000
Novartis Pharma AG
License And Royalty Revenue [Line Items]
License agreement upfront payment		$ 7,500,000
Revenue recognized upon achievement of related milestone			$ 2,500,000
Novartis Pharma AG \| Royalty
License And Royalty Revenue [Line Items]
Revenue													8,200,000	2,200,000
Novartis Pharma AG \| License and royalty revenue
License And Royalty Revenue [Line Items]
Cost of license and royalty revenue													3,000,000.0	900,000
Novartis Pharma AG \| Topic 606
License And Royalty Revenue [Line Items]
Number of performance obligation identified at the date of contract inception \| performance_obligation		1
Revenue												$ 7,500,000
Novartis Pharma AG \| Topic 606 \| Regulatory Milestones Payments
License And Royalty Revenue [Line Items]
Revenue												2,500,000
Orchard Therapeutics Limited
License And Royalty Revenue [Line Items]
License agreement upfront payment	$ 3,000,000.0
Orchard Therapeutics Limited \| License and royalty revenue
License And Royalty Revenue [Line Items]
Cost of license and royalty revenue													0	0
Orchard Therapeutics Limited \| Topic 606
License And Royalty Revenue [Line Items]
Number of performance obligation identified at the date of contract inception \| performance_obligation	1
Revenue												$ 3,000,000.0
Number of unsatisfied performance obligation identified at date of contract inception \| performance_obligation	0
Orchard Therapeutics Limited \| Topic 606 \| License
License And Royalty Revenue [Line Items]
Revenue													$ 0	$ 0
Regulatory Milestones Payments \| Novartis Pharma AG
License And Royalty Revenue [Line Items]
Amount per product eligible to be received upon achievement of specified event		$ 7,500,000
Each Subsequently Licensed Product \| Novartis Pharma AG
License And Royalty Revenue [Line Items]
Amount per product eligible to be received upon achievement of specified event		$ 1,100,000
Potential Milestones Payments \| Orchard Therapeutics Limited
License And Royalty Revenue [Line Items]
Amount per product eligible to be received upon achievement of specified event	$ 1,300,000