The Company and Basis of Presentation - Additional Information (Details)		1 Months Ended	6 Months Ended
	Apr. 12, 2016 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) Segment $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operating segments | Segment			1
Capital stock, 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
Preferred stock, shares outstanding | shares		0	0	0
Working capital		$ 61,800,000	$ 61,800,000
Accumulated deficit		(58,156,000)	(58,156,000)	$ (45,277,000)
Cash, cash equivalents and marketable securities		$ 63,400,000	$ 63,400,000
Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Proceeds from issuance of common stock upon initial public offering, net	$ 47,300,000
IPO
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Convertible preferred stock, terms of conversion			Ratio of one share of common stock for each share of convertible preferred stock
Convertible preferred stock converted into common stock | shares	7,172,496
Convertible preferred stock reclassified into common stock and additional paid-in-capital	$ 58,300,000
IPO | Common Stock
Organization Consolidation And Presentation Of Financial Statements [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
Underwriters' Over-allotment Option | Common Stock
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued | shares	481,940
Follow-on Public Offering | Common Stock | JonesTrading Institutional Services LLC
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of shares issued | shares		3,000,000
Public offering price | $ / shares		$ 4.10	$ 4.10
Proceeds from issuance of common stock upon initial public offering, net		$ 11,400,000
Underwriting discounts and commissions		615,000
Offering costs		306,000
Follow-on Public Offering | Common Stock | JonesTrading Institutional Services LLC | Outstanding Liability
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Offering costs payable		$ 186,000	$ 186,000