Business - Additional Information (Detail) - USD ($) $ in Thousands						1 Months Ended		3 Months Ended								12 Months Ended
	Jul. 29, 2019	Jul. 23, 2018	Jul. 18, 2018	Apr. 05, 2017	Mar. 30, 2017	Jul. 31, 2019	May 31, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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								89,000								89,000
Proceeds from sale of common stock in connection with license agreement																	$ 14,556
Unrestricted cash and cash equivalents and marketable securities								218,165								218,165
Accumulated deficit								400,727				$ 294,354				400,727	294,354
Net loss								$ 28,611	$ 32,842	$ 22,960	$ 21,960	$ 20,652	$ 19,400	$ 17,194	$ 16,767	106,373	74,013	$ 58,125
Net cash (used in) provided by operating activities																$ (109,225)	$ (22,301)	$ (54,827)
Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued																6,325,000	5,175,000	5,117,500
Common Stock [Member] | Follow-on Public Offering [Member]
Nature Of Business [Line Items]
Common stock, shares issued			5,175,000		5,117,500
Proceeds from issuance of common stock net	$ 136,498
Common Stock [Member] | Underwriter's Over-Allotment [Member]
Nature Of Business [Line Items]
Common stock, shares issued	825,000	675,000	675,000	667,500	667,500	825,000
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