Revenue Recognition - Disaggregation of Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 23,028	$ 135,082	$ 19,886
License and Milestone Fees
Disaggregation of Revenue [Line Items]
Total revenue	21,223	134,439	19,746
License and Milestone Fees | Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	15,000	22,262	19,746
License and Milestone Fees | Vifor International Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	5,031	111,551
License and Milestone Fees | Maruishi Pharmaceutical Co., Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	1,192
License and Milestone Fees | Chong Kun Dang Pharmaceutical Corp. [Member]
Disaggregation of Revenue [Line Items]
Total revenue		626
Collaborative Revenue
Disaggregation of Revenue [Line Items]
Total revenue	706
Collaborative Revenue | Maruishi Pharmaceutical Co., Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	706
Commercial Supply Revenue
Disaggregation of Revenue [Line Items]
Total revenue	701
Commercial Supply Revenue | Vifor International Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	701
Clinical Compound Revenue
Disaggregation of Revenue [Line Items]
Total revenue	398	643	140
Clinical Compound Revenue | Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	361	115
Clinical Compound Revenue | Maruishi Pharmaceutical Co., Ltd. [Member]
Disaggregation of Revenue [Line Items]
Total revenue	$ 37	$ 528	$ 140