Stock Award Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 16, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 6,857	$ 4,847	$ 5,135
Weighted average grant date fair value of the stock options granted	$ 1.51	$ 1.19	$ 3.05
Total intrinsic value of options exercised			$ 100
Cash received from the exercise of options		$ 10	500
Weighted-average remaining contractual term, options outstanding	7 years 9 months 21 days
Weighted-average remaining contractual term, options vested and expected to vest	5 years 7 months 13 days
Weighted-average remaining contractual term, options excerisable	5 years 6 months 25 days
Total intrinsic value of restricted stock units vested	$ 1,400	400	600
Fair value of restricted stock units vested	$ 2,400	1,900	2,600
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	10 years
Weighted average vesting period for unrecognized compensation expense	2 years 10 months 24 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Weighted average vesting period for unrecognized compensation expense	1 year 8 months 12 days
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	36 months
Vesting rights percentage	25.00%
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Restricted Stock | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights percentage	25.00%
Performance-based Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 1,900	$ 900	$ 300
Unrecognized compensation expense related to options	1,300
Options and Performance-based Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to options	8,500
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to non-option	$ 1,500
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity incentive plan, shares				12,000,000