Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member] Common Stock [Member]	Common Stock [Member] Common Stock Subscribed in Private Offering [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Stock Subscription Receivable [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance, Value at Dec. 31, 2019			$ 47	$ 587,223		$ (400,727)	$ 170	$ 186,713
Balance, Shares at Dec. 31, 2019			46,720,225
Stock-based compensation expense				2,846				2,846
Shares issued upon exercise of stock options, value				75				75
Shares issued upon exercise of stock options, shares			7,500
Net Loss						(28,922)		(28,922)
Other comprehensive income (loss)							(238)	(238)
Balance, Value at Mar. 31, 2020			$ 47	590,144		(429,649)	(68)	160,474
Balance, Shares at Mar. 31, 2020			46,727,725
Balance, Value at Dec. 31, 2019			$ 47	587,223		(400,727)	170	186,713
Balance, Shares at Dec. 31, 2019			46,720,225
Net Loss								(70,499)
Other comprehensive income (loss)							193
Balance, Value at Sep. 30, 2020			$ 47	598,663		(471,226)	363	127,847
Balance, Shares at Sep. 30, 2020			46,892,552
Balance, Value at Mar. 31, 2020			$ 47	590,144		(429,649)	(68)	160,474
Balance, Shares at Mar. 31, 2020			46,727,725
Stock-based compensation expense				2,993				2,993
Shares issued upon exercise of stock options, value				201				201
Shares issued upon exercise of stock options, shares			16,846
Shares issued upon vesting of restricted stock units, value				1,625				1,625
Shares issued upon vesting of restricted stock units, shares			119,834
Net Loss						(25,068)		(25,068)
Other comprehensive income (loss)							703	703
Balance, Value at Jun. 30, 2020			$ 47	594,963		(454,717)	635	140,928
Balance, Shares at Jun. 30, 2020			46,864,405
Stock-based compensation expense				3,305				3,305
Shares issued upon exercise of stock options, value				395				395
Shares issued upon exercise of stock options, shares			28,147
Net Loss						(16,509)		(16,509)
Other comprehensive income (loss)							(272)	(272)
Balance, Value at Sep. 30, 2020			$ 47	598,663		(471,226)	363	127,847
Balance, Shares at Sep. 30, 2020			46,892,552
Balance, Value at Dec. 31, 2020	$ 50			641,195		(392,317)	73	249,001
Balance, Shares at Dec. 31, 2020	49,872,213
Stock-based compensation expense				2,744				2,744
Shares issued upon exercise of stock options, value				688				688
Shares issued upon exercise of stock options, shares	45,035
Shares issued upon vesting of restricted stock units, value				1,388				1,388
Shares issued upon vesting of restricted stock units, shares	109,419
Net Loss						(23,301)		(23,301)
Other comprehensive income (loss)							(61)	(61)
Balance, Value at Mar. 31, 2021	$ 50			646,015		(415,618)	12	230,459
Balance, Shares at Mar. 31, 2021	50,026,667
Balance, Value at Dec. 31, 2020	$ 50			641,195		(392,317)	73	249,001
Balance, Shares at Dec. 31, 2020	49,872,213
Net Loss								(55,059)
Other comprehensive income (loss)							(72)
Common stock shares subscribed but unissued at Sep. 30, 2021		$ 3						$ 3
Common stock, shares subscribed but unissued (shares) at Sep. 30, 2021		3,282,391						3,282,391
Balance, Value at Sep. 30, 2021	$ 50			699,482	$ (44,969)	(447,376)	1	$ 207,191
Balance, Shares at Sep. 30, 2021	50,175,988
Balance, Value at Mar. 31, 2021	$ 50			646,015		(415,618)	12	230,459
Balance, Shares at Mar. 31, 2021	50,026,667
Stock-based compensation expense				3,376				3,376
Shares issued upon exercise of stock options, value				293				293
Shares issued upon exercise of stock options, shares	25,494
Shares issued upon vesting of restricted stock units, value				100				100
Shares issued upon vesting of restricted stock units, shares	36,000
Net Loss						(30,745)		(30,745)
Other comprehensive income (loss)							(17)	(17)
Balance, Value at Jun. 30, 2021	$ 50			649,784		(446,363)	(5)	203,466
Balance, Shares at Jun. 30, 2021	50,088,161
Subscription of common stock in Vifor stock purchase, value		$ 3		44,966	(44,969)
Subscription of common stock in Vifor stock purchase, shares		3,282,391
Stock-based compensation expense				3,487				3,487
Shares issued upon exercise of stock options, value				339				339
Shares issued upon exercise of stock options, shares	43,825
Shares issued upon vesting of restricted stock units, value				906				906
Shares issued upon vesting of restricted stock units, shares	44,002
Net Loss						(1,013)		(1,013)
Other comprehensive income (loss)							6	6
Common stock shares subscribed but unissued at Sep. 30, 2021		$ 3						$ 3
Common stock, shares subscribed but unissued (shares) at Sep. 30, 2021		3,282,391						3,282,391
Balance, Value at Sep. 30, 2021	$ 50			$ 699,482	$ (44,969)	$ (447,376)	$ 1	$ 207,191
Balance, Shares at Sep. 30, 2021	50,175,988