Collaboration and Licensing Agreements - Additional Information (Detail)		3 Months Ended		9 Months Ended
	May 17, 2018 USD ($) item $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer		$ 5,785,000	$ 5,062,000	$ 15,375,000	$ 7,936,000
Clinical Compound Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer			33,000	$ 140,000	33,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Non-refundable, non-creditable upfront payment	$ 50,000,000
Common stock, shares issued | shares	1,174,827
Purchase of common stock value	$ 20,000,000
Purchase common stock per share amount | $ / shares	$ 17.024
Closing prices of company common stock description	over a pre-determined average closing price of the Company's common stock
Premium from sale of stock	$ 5,444,000
Contract liabilities	$ 55,444,000
Number of combined performance obligations for revenue recognized | item	1
Number of days to terminate agreement				60 days
Termination notice effective period				12 months
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 470,000,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member] | Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	30,000,000
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Maximum [Member] | Tiered Commercial Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 440,000,000
Maruishi Pharmaceutical Co., Ltd. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost of clinical compound related to R&D expense			30,000	$ 126,000	30,000
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Compound Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue from contract with customer		$ 0	$ 33	$ 140,000	$ 33