Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		12 Months Ended
	Feb. 27, 2018	Mar. 26, 2018	Jan. 31, 2018	Dec. 31, 2017
IPO
Subsequent Event [Line Items]
Sale of common stock, shares				6,900,000
Offering price per share				$ 11.00
Subsequent Event | Almirall
Subsequent Event [Line Items]
Upfront license payment received		$ 30.0
Non-refundable portion of the upfront license payment received		$ 25.0
Subsequent Event | IPO
Subsequent Event [Line Items]
Sale of common stock, shares			4,300,000
Offering price per share			$ 15.25
Subsequent Event | Underwriters
Subsequent Event [Line Items]
Offering price per share	$ 15.25
Number of days granted to underwriters option to purchase additional shares			30 days
Number of additional common stock shares purchase	465,000
Net proceeds from stock issuance	$ 68.1
Underwriting discounts and commissions and offering expenses	$ 4.5
Subsequent Event | Underwriters | Maximum
Subsequent Event [Line Items]
Number of additional common stock shares purchase			645,000