Business - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 18, 2018	May 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
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			206,077		206,077
Accumulated deficit			273,702		273,702		$ 220,341
Net loss			$ 19,400	$ 12,444	53,361	$ 43,948
Net cash provided by (used in) operating activities					$ 2,060	$ (43,414)
Common Stock [Member]
Nature Of Business [Line Items]
Common stock, shares issued	5,175,000
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