Business - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Jul. 18, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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		182,779								182,779
Accumulated deficit		294,354				$ 220,341				294,354	$ 220,341
Net loss		$ 20,652	$ 19,400	$ 17,194	$ 16,767	$ 14,177	$ 12,444	$ 9,300	$ 22,204	74,013	58,125	$ 57,280
Net cash used in operating activities										(22,301)	$ (54,827)	$ (47,381)
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