Nature of Organization and Operations - Additional Information (Details)		1 Months Ended							12 Months Ended			144 Months Ended
	Dec. 12, 2018 shares	Apr. 30, 2019 Subject	Feb. 28, 2019 Subject	Mar. 31, 2018 shares	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2018 USD ($) Patient shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2018 USD ($) shares
Nature Of Organization And Operations [Line Items]
Proceeds from sale of stock												$ 468,400,000
Proceeds from issuance of public offering									$ 95,452,000	$ 114,580,000	$ 66,623,000
Number of months for operating plan sufficiently funded by cash resources									12 months
Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares | shares									9,194,306	8,672,270	7,865,293
Follow-on public offering
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of public offering												377,400,000
Follow-on public offering | Cantor Fitzgerald & Co
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of public offering												$ 41,000,000
Follow-on public offering | Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares | shares				8,500,000
Vifor Pharma | Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares | shares												3,571,429
Otsuka Pharmaceutical Co. Ltd. and Mitsubishi Tanabe Pharma Corporation
Nature Of Organization And Operations [Line Items]
Minimum committed amount in cost share funding and license payments under collaboration agreements									$ 573,000,000
Amount received from cost-share funding and license payments									$ 272,000,000
Merger Agreement | Keryx
Nature Of Organization And Operations [Line Items]
Issued and outstanding cancelled, converted common stock	0.37433
Number of shares cancelled and converted in merger, shares issued | shares	59,270,410
Protect and Innovate
Nature Of Organization And Operations [Line Items]
Number of patients | Patient									7,600
Larger Innovate Study | Subsequent Event
Nature Of Organization And Operations [Line Items]
Number of enrolled subjects | Subject			3,554
Smaller Innovate Study | Scenario Forecast
Nature Of Organization And Operations [Line Items]
Number of enrolled subjects | Subject		350
Development and Commercialize Collaboration Agreement | Mitsubishi Tanabe Pharma Corporation
Nature Of Organization And Operations [Line Items]
Collaborative arrangement right description									In December 2015, the Company entered into a collaboration agreement with Mitsubishi Tanabe Pharma Corporation, or MTPC, to develop and commercialize vadadustat in Japan and certain other countries in Asia, collectively, the MTPC Territory, for total payments of up to $245.0 million, comprised of a $20.0 million upfront payment, up to $50.0 million in specified development and regulatory milestones, and up to $175.0 million in specified commercial milestones, as well as tiered double-digit royalty payments up to 20% on sales of vadadustat in the MTPC Territory, subject to a reduction upon launch of a generic product on a country-by-country basis (Note 4).
Upfront cash payment received								$ 20,000,000	$ 20,000,000
Development and Commercialize Collaboration Agreement | Mitsubishi Tanabe Pharma Corporation | Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue								245,000,000
Additional milestone payments development costs fund								$ 50,000,000
Royalty payment percentage								20.00%
Development and Commercialize Collaboration Agreement | Mitsubishi Tanabe Pharma Corporation | Commercial Milestone Payments
Nature Of Organization And Operations [Line Items]
Milestone revenue								$ 175,000,000
Development and Commercialize Collaboration Agreement | Mitsubishi Tanabe Pharma Corporation | Commercial Milestone Payments | Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue									$ 175,000,000
Development and Commercialize Collaboration and License Agreement | Otsuka Pharmaceutical Company. Ltd.
Nature Of Organization And Operations [Line Items]
Upfront cash payment received					$ 73,000,000		$ 125,000,000
Development and Commercialize Collaboration and License Agreement | Otsuka Pharmaceutical Company. Ltd. | Global Development Plan
Nature Of Organization And Operations [Line Items]
Reimbursement for Otsuka's share of costs previously incurred					200,000	$ 33,800,000
Development and Commercialize Collaboration and License Agreement | Otsuka Pharmaceutical Company. Ltd. | Minimum | Global Development Plan
Nature Of Organization And Operations [Line Items]
Collaborative arrangements cost sharing payments					176,100,000		167,500,000
Development and Commercialize Collaboration and License Agreement | Otsuka Pharmaceutical Company. Ltd. | Potential Development and Commercialization Milestones | Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue					132,000,000		190,000,000
Development and Commercialize Collaboration and License Agreement | Otsuka Pharmaceutical Company. Ltd. | Potential Commercial Milestone Payments | Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue					$ 525,000,000		$ 575,000,000
License Agreement | Vifor Pharma
Nature Of Organization And Operations [Line Items]
Proceeds from sale of stock												$ 50,000,000
Restricted Stock Units | Merger Agreement | Keryx
Nature Of Organization And Operations [Line Items]
Number of shares cancelled and converted in merger, shares issued | shares	602,752
Stock Options | Merger Agreement | Keryx
Nature Of Organization And Operations [Line Items]
Number of shares cancelled and converted in merger, shares issued | shares	3,967,290