Collaboration Agreements (Takeda Collaboration, Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
Feb. 28, 2017	Dec. 28, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales volume period		6 years
Collaborative arrangement with Takeda
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment(s)	$ 50,000,000
Milestone payments earned		$ 10,000,000
Maximum amount eligible for development and regulatory milestones		90,000,000
Maximum amount eligible for commercial milestones under collaborations agreement		83,000,000
Remaining performance obligation		25,600,000
Net contract liability		$ 2,600,000
Collaborative arrangement with Takeda \| Global
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development arrangement performed for others, reimbursement for costs incurred, percent		20.00%
Collaborative arrangement with Takeda \| 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
Collaborative arrangement with Takeda \| Initial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty tier		$ 300,000,000.0
Collaborative arrangement with Takeda \| Minimum \| Initial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		15.00%
Collaborative arrangement with Takeda \| Minimum \| Final tier
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		20.00%
Collaborative arrangement with Takeda \| Maximum \| Initial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		24.00%
Collaborative arrangement with Takeda \| Maximum \| Final tier
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percent of royalty on net sale		30.00%

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

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