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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 05, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	29,500	38,500	139,000	174,000
Stock option expiration period			10 years
Options exercised			24,778
Intrinsic value of options exercised			$ 728
Stock-based compensation expense	$ 278	$ 168	$ 734	$ 344
Stock options available for grant	561,574		561,574
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 154	86	$ 396	$ 209
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period			4 years
Weighted-average grant-date fair value per share of options granted			$ 19.20
Unrecognized stock-based compensation expense	3,400		$ 3,400
Estimated weighted average period			3 years 2 months 15 days
Non-Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted			0	0
Non-Employee Stock Option [Member] \| Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	12	9	$ 33	$ 32
Non-Employee Stock Option [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period			1 year
Non-Employee Stock Option [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period			4 years
Employee's and Board Member's Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	266	159	$ 701	312
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period			1 year
Weighted-average grant-date fair value per share of options granted			$ 10.30
Stock-based compensation expense	$ 0	$ 109	$ 182	$ 109
Restricted stock award outstanding	0		0
Restricted Stock [Member] \| Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock award granted			26,213	26,213
Restricted Stock [Member] \| Chief Operating Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock award granted			16,213	16,213
2017 IPO Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorization to issue number of common stock					900,000