License, Collaboration and Other Significant Agreements - International Collaboration and License Agreement with Otsuka Pharmaceutical Co. Ltd. (Details) $ in Thousands		3 Months Ended			9 Months Ended
	Apr. 25, 2017 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2021 USD ($) performance_obligation	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue		$ 48,756	$ 59,988		$ 153,973	$ 238,608
Deferred revenue		43,657			43,657
Short-term deferred revenue		15,692			15,692		$ 15,214
Deferred revenue, net of current portion		27,965			27,965		25,345
Accounts receivable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable		21,413	2,761		21,413	2,761	3,045	$ 15,822
Prepaid expenses and other current assets
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable		3,442	1,248		3,442	1,248	1,722	0
Accounts payable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue		0	4,446		0	4,446	7,227	$ 0
License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue		12,003	25,596		$ 53,853	144,311
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of performance obligations | performance_obligation					3
Transaction price					$ 310,400
Reimbursement of costs				$ 200
Estimated current global development costs subsequent to March 31, 2017				$ 237,300
Deferred revenue		11,124			11,124
Short-term deferred revenue		4,501			4,501
Deferred revenue, net of current portion		6,623			6,623
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Accounts receivable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable		1,100			1,100
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Prepaid expenses and other current assets
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accounts receivable		1,100			1,100		500
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Accounts payable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue							$ 2,300
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | License, collaboration and other revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue		1,860	$ 7,243		13,532	$ 39,445
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Licensed HIF Product
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible milestone payments (up to)		17,000			$ 17,000
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Licensed HIF Product | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible milestone payments, period					12 months
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Licensed HIF Product | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible milestone payments, period					24 months
Otsuka Pharmaceutical Company. Ltd. | Otsuka International Agreement | Licensed Products
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Eligible milestone payments (up to)		$ 525,000			$ 525,000
Otsuka Pharmaceutical Company. Ltd. | Up Front Non Refundable And Non Creditable | Otsuka International Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment received	$ 73,000