Collaboration Agreements - Takeda Collaboration (Details) - Collaborative Arrangement with Takeda - USD ($)		9 Months Ended
Jan. 01, 2017	Sep. 28, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment(s)	$ 50,000,000
Maximum amount eligible for development and regulatory milestones		$ 100,000,000
Maximum pre-specified payments		$ 83,000,000
Sales volume period		6 years
Remaining performance obligation		$ 28,500,000
Net contract liability		$ 2,300,000
Global
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development arrangement performed for others, reimbursement for costs incurred, percent		20.00%
Japan
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development arrangement performed for others, reimbursement for costs incurred, percent		100.00%
Collaboration period to achieve specified levels of commercial performance		2 years
Initial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cumulative net sales		$ 300,000,000.0
Initial \| Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		15.00%
Initial \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		24.00%
Final \| Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		20.00%
Final \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		30.00%

Collaborative Arrangement, Achievement Levels of Commercial Performance, Period

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Maximum amount eligible for development and regulatory milestones under collaborations agreement.

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Maximum amount eligible for commercial milestones under collaborations agreement.

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Percent of royalty on net sale.

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Research and Development Arrangement Performed for Others, Reimbursement for Costs Incurred, Percent

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Upfront Payment(s)

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

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