Commitments and Contingencies - Narrative (Details)						1 Months Ended				3 Months Ended				12 Months Ended
	Feb. 10, 2021	Sep. 04, 2020	Apr. 02, 2020	Apr. 09, 2019	Jan. 01, 2017 USD ($)	Dec. 31, 2021 USD ($) ft² extensionOption	Dec. 31, 2020 USD ($)	Feb. 28, 2019 USD ($)	Jul. 31, 2016 USD ($) ft²	Dec. 31, 2021 USD ($) ft² extensionOption	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) ft² extensionOption	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Nov. 30, 2020 ft²	Apr. 30, 2018 ft²
Commitments And Contingencies [Line Items]
Operating lease, cost														$ 6,700,000	$ 6,700,000
Operating lease, payments														7,100,000	7,000,000
Charge to cost of goods sold										$ 18,000,000		$ 30,300,000
Receipts related to inventory														25,847,000	(6,163,000)	$ 29,142,000
Decrease in purchase commitments											$ 6,000,000			(33,391,000)	(25,114,000)	$ 0
Total remaining contract costs						$ 5,000,000				5,000,000				5,000,000
Contract cost incurred in research and development activities														237,800,000
Supply Agreement, Patheon Inc.
Commitments And Contingencies [Line Items]
Minimum purchase commitment						4,000,000				4,000,000				4,000,000
Keryx Biopharmaceuticals, Inc.
Commitments And Contingencies [Line Items]
Preliminary fair value of the off-market element						76,700,000	$ 55,800,000			76,700,000				76,700,000	55,800,000
Decrease in purchase commitments													$ 8,900,000
Cambridge
Commitments And Contingencies [Line Items]
Area of property leased | ft²									45,362								65,167
Annual operating lease expense									$ 242,000
Monthly operating lease expense					$ 22,000
BioVectra Inc
Commitments And Contingencies [Line Items]
Long-term minimum purchase commitment renewal term		1 year
Cost of purchased minimum quantity product						83,600,000				83,600,000				83,600,000
Siegfried Evionnaz SA
Commitments And Contingencies [Line Items]
Cost of purchased minimum quantity product						$ 15,600,000				$ 15,600,000				$ 15,600,000
Purchase commitment, option to extend, prior notice period														12 months
Esteve Química, S.A
Commitments And Contingencies [Line Items]
Long-term purchase commitment														$ 28,900,000
Initial term of supply agreement				4 years
STA Pharmaceutical Hong Kong Limited
Commitments And Contingencies [Line Items]
Long-term purchase commitment														$ 29,200,000
Long-term purchase commitment, initial term			4 years
WuXi STA
Commitments And Contingencies [Line Items]
Purchase commitment, option to extend, prior notice period	18 months
Long-term purchase commitment, initial term	4 years
Long-term purchase commitment, fixed price, period	12 months
Long-term purchase commitment, option to terminate, prior notice period (at least)	180 days
Minimum
Commitments And Contingencies [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term						6.65%				6.65%				6.65%
Operating lease, remaining lease term						4 years 8 months 12 days				4 years 8 months 12 days				4 years 8 months 12 days
Maximum
Commitments And Contingencies [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term						7.25%				7.25%				7.25%
Operating lease, remaining lease term						9 years 7 months 2 days				9 years 7 months 2 days				9 years 7 months 2 days
Letter of Credit | Other Current Assets | Keryx Biopharmaceuticals, Inc.
Commitments And Contingencies [Line Items]
Total security deposit in connection with lease						$ 400,000				$ 400,000				$ 400,000
Letter of Credit | Other Current Assets | Cambridge
Commitments And Contingencies [Line Items]
Total security deposit in connection with lease						1,600,000				$ 1,600,000				$ 1,600,000
Office Space | Cambridge
Commitments And Contingencies [Line Items]
Area of property leased | ft²																		19,805
Monthly operating lease expense						$ 48,000		$ 135,000
Operating lease, free monthly rent, period							2 months
Operating lease period, number of extension options | extensionOption						1				1				1
Operating lease extension period						5 years				5 years				5 years
Office Space | Boston
Commitments And Contingencies [Line Items]
Area of property leased | ft²						27,300				27,300				27,300
Monthly operating lease expense														$ 136,000
Office Space | Boston | Keryx Biopharmaceuticals, Inc.
Commitments And Contingencies [Line Items]
Operating lease period, number of extension options | extensionOption						1				1				1
Operating lease extension period						5 years				5 years				5 years
Sublease rent payments received														$ 1,800,000	$ 1,800,000
Lab Space | Cambridge
Commitments And Contingencies [Line Items]
Operating lease period, number of extension options | extensionOption						1				1				1