Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands						1 Months Ended	12 Months Ended
	Jul. 23, 2018	Jul. 18, 2018	May 17, 2018	Apr. 05, 2017	Mar. 30, 2017	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Common stock, shares authorized						100,000,000	100,000,000	100,000,000
Common stock, par value						$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized						5,000,000	5,000,000	5,000,000
Preferred stock, par value						$ 0.001	$ 0.001	$ 0.001
Common stock, shares outstanding						39,547,558	39,547,558	32,662,255
Preferred stock, shares issued						0	0	0
Preferred stock, shares outstanding						0	0	0
Conversion of shares						83,791
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued			1,174,827
Public offering price per share			$ 17.024
Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		5,175,000
Conversion of shares							83,791
Common Stock [Member] | Follow-on Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued					5,117,500		5,175,000	5,117,500
Public offering price per share		$ 19.00			$ 18.00	$ 19.00	$ 19.00	$ 18.00
Proceeds from issuance of common stock net of underwriting discounts and offering costs	$ 92,063			$ 86,224
Underwriting discounts, commission and offering expenses	$ 6,262			$ 5,891
Common Stock [Member] | Underwriter's Over-Allotment [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		675,000
Common Stock [Member] | Underwriter's Over-Allotment [Member] | Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	675,000			667,500	667,500