Stockholders' Equity - Additional Information (Detail) - USD ($) $ in Thousands						1 Months Ended	6 Months Ended
	Jul. 23, 2018	Jul. 18, 2018	May 18, 2018	May 17, 2018	Apr. 05, 2017	Jul. 31, 2018	Jun. 30, 2017
Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of common stock net of underwriting discounts and offering costs	$ 92,026
Underwriting discounts, commission and offering expenses	$ 6,300
Vifor Fresenius Medical Care Renal Pharma Ltd. [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued			1,174,827	1,174,827
Follow-on Public Offering [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of common stock net of underwriting discounts and offering costs						$ 92,026
Common Stock [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		5,175,000
Common Stock [Member] | Follow-on Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued					5,117,500		5,117,500
Proceeds from issuance of common stock net of underwriting discounts and offering costs					$ 86,224
Underwriting discounts, commission and offering expenses					$ 5,891
Common Stock [Member] | Follow-on Public Offering [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	5,175,000					5,175,000
Proceeds from issuance of common stock net of underwriting discounts and offering costs	$ 92,026
Underwriting discounts, commission and offering expenses	$ 6,300
Common Stock [Member] | Underwriter's Over-Allotment [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	675,000	675,000				675,000
Common Stock [Member] | Underwriter's Over-Allotment [Member] | Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued					667,500
Common Stock [Member] | Underwriter's Over-Allotment [Member] | Maximum [Member] | Subsequent Event [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued	675,000