Business - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended						9 Months Ended
	Oct. 15, 2020	May 31, 2018	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 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			131,375						131,375
Accumulated deficit			471,226						471,226		$ 400,727
Net loss			$ 16,509	$ 25,068	$ 28,922	$ 32,842	$ 22,960	$ 21,960	70,499	$ 77,762
Net cash used in operating activities									$ (87,575)	$ (78,059)
Vifor International Ltd. [Member]
Nature Of Business [Line Items]
Proceeds from sale of common stock in connection with license agreement		$ 14,556
Vifor International Ltd. [Member] | Subsequent Event [Member] | Exclusive License Agreement [Member]
Nature Of Business [Line Items]
Common stock, shares issued	2,939,552
Non-refundable, non-creditable upfront payment	$ 100,000
Purchase of common stock value	$ 50,000
Vifor International Ltd. [Member] | Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued		1,174,827