Stock-Based Compensation and Employee Stock Purchase Program - Additional Information (Detail)						1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 19, 2021	Dec. 14, 2021	May 17, 2021 shares	May 20, 2015 shares	May 14, 2015	Jun. 30, 2019 shares	Sep. 30, 2018	Dec. 31, 2021 USD ($) IncentivePlan $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity incentive plans | IncentivePlan								2
Shares Subject to Outstanding, Options granted								1,227,042	502,494
Total number of options outstanding								1,422,195	889,759	661,701
Intrinsic value of options exercisable | $								$ 0	$ 0
Unrecognized compensation cost related to unvested stock-based compensation grants | $								$ 1,100,000
Weighted-average remaining recognition period								3 years
Stock-based compensation | $								$ 1,541,000	$ 2,042,000
Weighted-average estimated grant-date fair value of stock options granted | $ / shares								$ 2.41	$ 3.80
2015 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance under plan								111,722
Stock-based compensation | $								$ 14,000	$ 47,000
Percentage in payroll deductions to acquire shares of common stock					15.00%
Purchase plan offering period					6 months
Employees are able to purchase company's common stock on first trading day of offering period, percentage					85.00%
Issuance of common stock pursuant to employee stock purchase plan								50,245
First offering period, start date					May 14, 2015
First offering period, end date					Feb. 01, 2016
Separation Agreement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable period	2 years 6 months	90 days
Separation Agreement [Member] | Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation | $								$ 154,000
Inducement Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Subject to Outstanding, Options granted			248,000
Total number of options outstanding								68,000
2015 Omnibus Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Terms under the plan								The 2015 Plan became effective upon the Company’s IPO in May 2015 and all shares that were reserved, but not issued, under the 2006 Plan were assumed by the 2015 Plan. Upon effectiveness, the 2015 Plan had 154,387 shares of common stock reserved for future issuance, which included 10,637 that were transferred to and assumed by the 2015 Plan. The 2015 Plan provides for automatic annual increases in shares available for grant. In addition, shares subject to awards under the 2006 Plan that are forfeited or canceled will be added to the 2015 Plan.
Total number of shares reserved for issuance under plan				154,387				1,596,209
Options vesting period				4 years			2 years
Additional shares authorized for issuance under the plan						120,000
Common stock available for future grant								250,254
Total number of options outstanding								1,345,955
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance under plan				10,637
Total number of options outstanding								8,240
Maximum [Member] | 2015 Omnibus Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable period				10 years