Business - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended
	May 31, 2018	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Nature Of Business [Line Items]
Date of formation						Jul. 02, 2004
Proceeds from equity and debt financing		$ 519,600				$ 519,600
Upfront and milestone payments received in connection with license agreements		90,300				90,300
Unrestricted cash and cash equivalents and marketable securities		153,046				153,046
Accumulated deficit		454,717				454,717		$ 400,727
Net loss		$ 25,068	$ 28,922	$ 22,960	$ 21,960	53,990	$ 44,920
Net cash used in operating activities						$ (65,955)	$ (52,422)
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Nature Of Business [Line Items]
Proceeds from sale of common stock in connection with license agreement	$ 14,556
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member] | Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued	1,174,827