STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income.	Total
Balance, Value at Dec. 31, 2019	$ 47	$ 587,223	$ (400,727)	$ 170	$ 186,713
Balance, Shares at Dec. 31, 2019	46,720,225
Sale of common stock under license agreement with Vifor International, value	$ 3	38,446			38,449
Sale of common stock under license agreement with Vifor International, shares	2,939,552
Stock-based compensation expense		12,486			12,486
Shares issued upon exercise of stock options, value		691			691
Shares issued upon exercise of stock options, shares	55,852
Shares issued upon vesting of restricted stock units, value		2,349			2,349
Shares issued upon vesting of restricted stock units, shares	156,584
Net income (loss)			8,410		8,410
Other comprehensive loss				(97)	(97)
Balance, Value at Dec. 31, 2020	$ 50	641,195	(392,317)	73	249,001
Balance, Shares at Dec. 31, 2020	49,872,213
Sale of common stock under license agreement with Vifor International, value	$ 3	44,966			44,969
Sale of common stock under license agreement with Vifor International, shares	3,282,391
Stock-based compensation expense		17,850			17,850
Shares issued upon exercise of stock options, value		1,639			1,639
Shares issued upon exercise of stock options, shares	136,787
Shares issued upon vesting of restricted stock units, value		2,935			2,935
Shares issued upon vesting of restricted stock units, shares	189,421
Net income (loss)			(88,441)		(88,441)
Other comprehensive loss				(431)	(431)
Balance, Value at Dec. 31, 2021	$ 53	708,585	(480,758)	(358)	227,522
Balance, Shares at Dec. 31, 2021	53,480,812
Stock-based compensation expense		14,345			14,345
Shares issued upon exercise of stock options, value		311			$ 311
Shares issued upon exercise of stock options, shares	48,307				48,307
Shares issued upon vesting of restricted stock units, value		3,389			$ 3,389
Shares issued upon vesting of restricted stock units, shares	268,222
Net income (loss)			(85,474)		(85,474)
Other comprehensive loss				(1,314)	(1,314)
Balance, Value at Dec. 31, 2022	$ 53	$ 726,630	$ (566,232)	$ (1,672)	$ 158,779
Balance, Shares at Dec. 31, 2022	53,797,341