Revenue Recognition - Additional Information (Detail) ¥ in Billions			1 Months Ended		3 Months Ended								12 Months Ended			32 Months Ended
	Oct. 15, 2020 item	May 17, 2018 USD ($) item	Apr. 30, 2013 USD ($) item	Apr. 30, 2012 USD ($) item	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) contract item	Dec. 31, 2019 USD ($) Milestone	Dec. 31, 2018 USD ($) Milestone	Dec. 31, 2020 USD ($)	Apr. 30, 2013 JPY (¥)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue, current									$ 22,262,000					$ 22,262,000
Number of contracts | contract													4
Total revenue					$ 112,089,000	$ 9,266,000	$ 5,634,000	$ 8,093,000	4,511,000	$ 5,785,000	$ 5,208,000	$ 4,382,000	$ 135,082,000	19,886,000	$ 13,469,000
License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue													134,439,000	19,746,000	$ 13,436,000
Royalty [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from contract with customer													0
Vifor Agreement [Member] | License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue					111,551,000								111,551,000
Number of performance obligations for revenue recognized | item	1
upfront payment													100,000,000
Premium from sale of stock													11,551,000
Revenue from contract with customer													111,551,000
Remaining performance obligations					0								0			$ 0
VFMCRP Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue, current									22,262,000					22,262,000
Receivables									0					0
Other assets									0					0
Deferred revenue									0					0
Number of combined performance obligations for revenue recognized | item		1
Number of performance obligations for revenue recognized | item		2
upfront payment		$ 50,000,000
Premium from sale of stock		5,444,000
VFMCRP Agreement [Member] | License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue		$ 55,444,000
Total revenue													22,262,000			55,444,000
Number of performance obligations for revenue recognized | item		1
Remaining performance obligations					0								0			0
Vifor, VFMCRP, Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Receivables					0								0			0
Other assets					0								0			0
Deferred revenue					0								$ 0			0
Vifor, Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
License agreements with IP as separate performance obligation | item													3
Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Receivables									0					0
Other assets									0					0
Deferred revenue									$ 0					$ 0
Remaining performance obligations					$ 0								$ 0			$ 0
Maruishi Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of performance obligations for revenue recognized | item			2
Premium from sale of stock			$ 337,000
Upfront non-refundable, non-creditable license fee and premium from sale of stock			15,337,000
Maruishi Agreement [Member] | Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential milestone payments			10,500,000
Maruishi Agreement [Member] | One-time Sales Milestone [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential milestone payments | ¥																	¥ 1
Maruishi Agreement [Member] | License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated selling price			10,200,000
Upfront payments on obligations			9,637,000
Maruishi Agreement [Member] | R&D Services [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated selling price			6,200,000
Upfront payments on obligations			$ 5,700,000
CKDP Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of performance obligations for revenue recognized | item				1
Premium from sale of stock				$ 83,000
Number of milestone event probable of occurrence or achieved | Milestone														0	0
CKDP Agreement [Member] | Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Potential milestone payments				3,750,000
CKDP Agreement [Member] | License and Milestone Fees
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue													$ 626,000
CKDP Agreement [Member] | License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from contract with customer				$ 646,000
Maruishi Pharmaceutical Co., Ltd. [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of performance obligations for revenue recognized | item			2