Stock Option Plan - Additional information (Detail) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended			12 Months Ended
	Nov. 21, 2019	Aug. 19, 2019	Jul. 22, 2019	Sep. 30, 2019	Jan. 31, 2019	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance							5,842,879
Outstanding options issued							5,842,879	5,277,085	3,852,135	3,465,335
Proceeds from stock options exercised							$ 1,219	$ 240	$ 88
Total intrinsic value of options							$ 1,100	$ 100	$ 200
Stock options, granted							2,880,691	1,744,950	688,800
Stock options granted exercise price							$ 3.40	$ 2.35	$ 5.27
Options available for future grant							2,503,508
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of shares of restricted common stock							225,339	514,349	394,269
restricted stock in lieu					446,428
Restricted Stock | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of shares of restricted common stock, price per share							$ 4.72	$ 4.41	$ 7.12
Restricted Stock | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of shares of restricted common stock, price per share							$ 2.24	$ 1.70	$ 4.14
Restricted Stock | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award granted					947,108			30,000	838,000
Restricted Stock | Non Employee Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment award granted				15,000			111,230	120,321	69,032
Unvested Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs related to non-vested restricted stock outstanding							$ 9,000
Expected recognition period							1 year 9 months 10 days
Unvested Restricted Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected recognition period							1 year 3 months 14 days
Share-based payment award granted							1,519,766	150,321	907,032
Unrecognized stock-based compensation expense related to non-vested restricted stock arrangements							$ 2,700
the "2012 Plan"
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance							14,000,000
the "2012 Plan" | Employees | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding options issued							4,550,071
the "2012 Plan" | Director | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding options issued							1,282,808
the "2012 Plan" | Consultants | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding options issued							10,000
Outside 2012 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance							1,030,000
Outstanding options issued							1,030,000
Stock options, granted	65,000	65,000	400,000			500,000
Stock options granted exercise price	$ 4.59	$ 5.18	$ 5.60			$ 6.16
Share Based compensation arrangement by share based payment award options grants grant date fair value	$ 193	$ 231	$ 1,500			$ 2,200