Accounting policy.

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Highly liquid investment maturity period.

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Long term investments minimum maturity period.

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Restricted time deposits noncurrent.

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Short term investments maximum maturity period.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in estimate of transaction price which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due. Includes, but is not limited to, change in assessment of whether estimate of variable consideration is constrained.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended
	Nov. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017
Accounting Policy [Line Items]
Number of operating segment \| Segment		1
Highly liquid investment maturity period		three months or less
Restricted time deposits		$ 2,072,000	$ 4,145,000
Cash and cash equivalents		$ 126,266,000	$ 89,258,000
Short term investments maturity		12 months
Long term Investments Maturity		12 months
Impairment of long-lived assets		$ 0
U.S. federal statutory income tax rate		21.00%	21.00%	34.00%
Japan [Member] \| Astellas Agreement [Member]
Accounting Policy [Line Items]
Difference in estimated and actual listed price	$ 36,300,000	$ 36,300,000
U.S. federal statutory income tax rate		21.00%		35.00%
Minimum [Member] \| Computer Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		3 years
Minimum [Member] \| Laboratory Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		3 years
Minimum [Member] \| Machinery [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		3 years
Maximum [Member]
Accounting Policy [Line Items]
U.S. federal statutory income tax rate				35.00%
Maximum [Member] \| Computer Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		5 years
Maximum [Member] \| Laboratory Equipment [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		5 years
Maximum [Member] \| Machinery [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		5 years
Maximum [Member] \| Furniture and Fixtures [Member]
Accounting Policy [Line Items]
Property and equipment estimated useful life		5 years
Foreign subsidiaries [Member]
Accounting Policy [Line Items]
Cash and cash equivalents		$ 11,900,000	$ 21,900,000