Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	9 Months Ended		12 Months Ended
	Jun. 16, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance		3,113,310	3,113,310		12,206,216
Common stock, weighted average exercise price per share			$ 10.50
Weighted average grant-date fair value of stock options			$ 7.51	$ 3.24
Aggregate fair value of stock options vested			$ 810	$ 718
Aggregate intrinsic value of stock options exercised			256	$ 6
Aggregate unrecognized stock-based compensation expense		$ 9,114	$ 9,114
Unrecognized stock-based compensation expense, weighted average period expects for recognition			3 years 6 months
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase			3,750,000
2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period			4 years
Number of shares, available for grant		1,244,816	1,244,816
Maximum annual increase in common stock reserved for future issuance			1,244,816
Percentage of common stock shares outstanding			4.00%
Options to purchase		619,027
Common stock, weighted average exercise price per share		$ 12.80
2016 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period			4 years
Stock option expiration period			10 years
Common stock, shares authorized for issuance		0	0
2016 Stock Incentive Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance		424,601	424,601
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance	150,000
Maximum annual increase in common stock reserved for future issuance	622,408
Percentage of common stock shares outstanding	1.00%
Stock incentive plan description			On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors.
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period					4 years
Stock option expiration period					10 years
Stock incentive plan termination year					2016
Maximum [Member] | 2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period			4 years
Stock option expiration period			10 years
Maximum [Member] | 2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period					4 years