Stockholder's Equity - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Oct. 12, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 1,048,000	$ 2,820,000
Restricted stock unit remaining weighted average period	7 years 2 months 12 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	$ 5.52
Tax benefits realized from options and other share-based payment arrangements	$ 0
Weighted-average remaining vesting period	3 years 6 months
Unrecognized employee stock-based compensation	$ 3,300,000
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	400,000	$ 1,200,000
Approximate compensation expenses	$ 1,900,000
Restricted stock unit remaining weighted average period	2 years
2014 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	711,484
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
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
Number of shares reserved			600,000
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
Number of shares reserved			461,000
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%