Convertible Preferred Stock and Stockholders' Equity - Additional Information (Details)			1 Months Ended					12 Months Ended
	Apr. 12, 2016 USD ($) $ / shares shares	Apr. 05, 2016 USD ($) shares	Dec. 31, 2018 USD ($) Vote $ / shares shares	Oct. 31, 2018 USD ($) $ / shares shares	Apr. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares	May 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Vote $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Class Of Stock [Line Items]
Preferred stock, shares outstanding | shares			0					0	0
Convertible preferred stock, terms of conversion		all of the outstanding convertible preferred stock was automatically converted into 7,172,496 shares of common stock on a one-to-one basis
shares authorized | shares	510,000,000
Common stock, shares authorized | shares	500,000,000		500,000,000					500,000,000	500,000,000
Preferred stock, shares authorized | shares	10,000,000		10,000,000					10,000,000	10,000,000
Common stock, par value | $ / shares	$ 0.0001		$ 0.0001					$ 0.0001	$ 0.0001
Preferred stock, par value | $ / shares	$ 0.0001		$ 0.0001					$ 0.0001	$ 0.0001
Number of common stock holders voting right | Vote			1					1
Common stock voting rights								Each holder of common stock is entitled to one vote for each share of common stock held
Common stock dividends declared								$ 0
Proceeds from issuance of common stock in public offering, net								$ 54,048,000	$ 11,380,000	$ 47,266,000
At-the-Market (ATM) Sales Agreement | JonesTrading Institutional Services LLC
Class Of Stock [Line Items]
Number of shares issued | shares				1,845,820
Public offering price | $ / shares				$ 9.21
Aggregate offering price of common stock							$ 20,000,000
Net proceeds from sale of common stock				$ 16,400,000
Proceeds from issuance of common stock gross				$ 17,000,000
At-the-Market (ATM) Sales Agreement | Jeffries LLC
Class Of Stock [Line Items]
Aggregate offering price of common stock			$ 60,000,000
Common Stock
Class Of Stock [Line Items]
Convertible preferred stock converted into common stock | shares		7,172,496
Convertible preferred stock converted into common stock, carrying value		$ 58,300,000
Number of shares issued | shares					5,046,510			6,893,000	3,000,000	5,482,000
Proceeds from issuance of common stock upon initial public offering, net	$ 47,300,000
Underwriting discounts and commissions					$ 2,400,000
Offering costs					$ 300,000
Public offering price | $ / shares					$ 8.00
Proceeds from issuance of common stock in public offering, net									$ 1,000
Common Stock | IPO
Class Of Stock [Line Items]
Number of shares issued | shares	5,481,940
Public offering price | $ / shares	$ 10.00
Underwriting discounts and commissions	$ 3,800,000
Offering costs	$ 3,700,000
Common Stock | Underwriters' Over-allotment Option
Class Of Stock [Line Items]
Number of shares issued | shares	481,940				546,510
Common Stock | Follow-on Public Offering
Class Of Stock [Line Items]
Proceeds from issuance of common stock in public offering, net					$ 37,700,000
Common Stock | Follow-on Public Offering | JonesTrading Institutional Services LLC
Class Of Stock [Line Items]
Number of shares issued | shares						3,000,000
Underwriting discounts and commissions						$ 600,000
Offering costs						$ 300,000
Public offering price | $ / shares						$ 4.10
Proceeds from issuance of common stock in public offering, net						$ 11,400,000
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares outstanding | shares											2,172,520
Preferred stock outstanding carrying value											$ 13,600,000
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares outstanding | shares											4,999,976
Preferred stock outstanding carrying value											$ 44,700,000