Stockholder's Equity - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Oct. 12, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 941,000	$ 2,155,000	$ 1,989,000	$ 4,975,000
Restricted stock unit remaining weighted average period			7 years 1 month 6 days
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			4 years
Stock options, weighted-average grant date fair value			$ 4.69
Tax benefits realized from options and other share-based payment arrangements			$ 0
Weighted-average remaining vesting period			3 years 4 months 24 days
Unrecognized employee stock-based compensation	2,800,000		$ 2,800,000
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 400,000	$ 700,000	800,000	$ 1,900,000
Approximate compensation expenses			$ 1,500,000
Restricted stock unit remaining weighted average period			1 year 7 months 6 days
2014 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	723,462		723,462
Percentage of common stock issued and outstanding increase annually			4.50%
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of common stock issued and outstanding increase annually			1.00%
Number of shares reserved	150,000		150,000
Additional shares issued			300,000
2010 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	108,839		108,839
Number of shares reserved					1,368,060
Options vested , description			Options granted to employees and consultants under the Plan generally vest 25% after one year of service, and ratably on a monthly basis over the following three years. Options expire ten years from the date of grant.
Options expiration period			10 years
Options vesting period			3 years
Employee service term for options granted			1 year
2010 Plan [Member] | After One Year of Service [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vested percentage			25.00%
2017 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	551,133		551,133
Number of shares reserved					1,051,544
Options vested , description			Options granted to employees and consultants under the Plan generally vest 25% after one year of service, and ratably on a monthly basis over the following three years. Options expire ten years from the date of grant.
Options expiration period			10 years
Options vesting period			3 years
Employee service term for options granted			1 year
2017 Plan [Member] | After One Year of Service [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vested percentage			25.00%