Revenue Recognition - Additional Information (Detail) ¥ in Billions		1 Months Ended		3 Months Ended		9 Months Ended
	May 17, 2018 USD ($) item	Apr. 30, 2013 USD ($) item	Apr. 30, 2012 USD ($)	Sep. 30, 2019 USD ($) Milestone	Sep. 30, 2018 USD ($) Milestone	Sep. 30, 2019 USD ($) Milestone item	Sep. 30, 2018 USD ($) Milestone	Dec. 31, 2018 USD ($)	Apr. 30, 2013 JPY (¥)	Apr. 30, 2013 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue, current				$ 26,773,000		$ 26,773,000		$ 26,825,000
Deferred revenue, non current				0		0		15,184,000
Total revenue				$ 5,785,000	$ 5,062,000	$ 15,375,000	$ 7,936,000
Number of milestone event probable of occurrence or achieved | Milestone				0	0	0	0
License and Milestone Fees [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue				$ 5,785,000	$ 5,029,000	$ 15,235,000	$ 7,903,000
Royalty [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from contract with customer						0
VFMCRP Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Deferred revenue, current				26,773,000		26,773,000		26,825,000
Deferred revenue, non current								15,184,000
Receivables				0		0
Other assets								0
Deferred revenue	$ 55,444,000
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
Remaining performance obligations				$ 26,773,000		$ 26,773,000
Remaining performance obligation, expected timing of satisfaction, year				2020		2020
VFMCRP Agreement [Member] | License and Milestone Fees [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Total revenue				$ 5,785,000		$ 15,235,000
License and milestone fees recognized						28,671,000
Maruishi and CKDP Agreements [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Receivables				$ 0		$ 0
Other assets								0
Deferred revenue								$ 0
Number of remaining performance obligations | item						0
Maruishi Agreement [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of performance obligations for revenue recognized | item		2				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]
Remaining potential consideration										$ 10,500,000
Maruishi Agreement [Member] | One-time Sales Milestone [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Remaining potential consideration | ¥									¥ 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]
Premium from sale of stock			$ 83,000
CKDP Agreement [Member] | Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Remaining potential consideration			3,750,000
CKDP Agreement [Member] | License [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from contract with customer			$ 646,000