License, Collaboration and Other Significant Agreements - Vifor Pharma License Agreement (Details) $ / shares in Units, $ in Thousands						3 Months Ended
	Feb. 22, 2022 USD ($) $ / shares shares	Feb. 18, 2022 USD ($)	Feb. 14, 2020 USD ($)	Apr. 08, 2019 USD ($)	May 12, 2017 USD ($) $ / shares shares	Mar. 31, 2022 USD ($) performance_obligation $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment						$ 75,796
Common stock, issued (in shares) | shares						183,386,035	177,000,963
Common stock, par value (in dollars per share) | $ / shares	$ 0.00001					$ 0.00001	$ 0.00001
Current portion of refund liability to customer						$ 16,500	$ 0
Vifor (International) Ltd.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract termination, prior written notice period		30 months
Contract termination, period subsequent complete response letter		30 days
Private Placement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of shares sold in offering (in shares) | shares	4,000,000
Aggregate net proceeds from offering	$ 20,000
Aggregate net proceeds from offering, fair value in excess of carrying amount	$ 13,600
Vifor (International) Ltd.
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract termination, prior written notice period		6 months
Refund liability to customer, gross						40,000
Refund liability to customer, net of deferred gain and discount						$ 39,900
Vifor (International) Ltd. | License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue, remaining performance obligation, profit share percentage		66.00%
Upfront payment		$ 25,000
Number of performance obligations | performance_obligation						1
Refund liability to customer, purchase orders to total						50.00%
Refund liability to customer, interest rate						15.00%
Vifor (International) Ltd. | License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone revenue				$ 25,000
Common stock, issued (in shares) | shares					3,571,429
Sale of stock, price per share (in dollars per share) | $ / shares					$ 14.00
Proceeds from common stock sold					$ 50,000
Premium over the closing stock price of common stock (in dollars per share) | $ / shares					$ 12.69
Premium amount over the closing stock price of common stock					$ 4,700
Vifor (International) Ltd. | Priority Review Voucher Letter Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payments for closing Priority Review Voucher purchase			$ 10,000
Proceeds from collaborators							$ 8,600