Business - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended				6 Months Ended
	Jul. 29, 2019	Jul. 31, 2019	May 31, 2018	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Nature Of Business [Line Items]
Date of formation								Jul. 02, 2004
Proceeds from equity and debt financing				$ 383,200				$ 383,200
Upfront and milestone payments received in connection with license agreements				88,900				88,900
Proceeds from sale of common stock in connection with license agreement									$ 14,556
Unrestricted cash and cash equivalents and marketable securities				135,629				135,629
Accumulated deficit				339,274				339,274		$ 294,354
Net loss				$ 22,960	$ 21,960	$ 17,194	$ 16,767	44,920	33,961
Net cash (used in) provided by operating activities								$ (52,422)	$ 22,552
Common Stock [Member] | Follow-on Public Offering [Member] | Subsequent Event [Member]
Nature Of Business [Line Items]
Common stock, shares issued	6,325,000	6,325,000
Proceeds from issuance of common stock net	$ 136,446	$ 136,446
Common Stock [Member] | Underwriter's Over-Allotment [Member] | Subsequent Event [Member]
Nature Of Business [Line Items]
Common stock, shares issued	825,000	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