STOCKHOLDERS' EQUITY - Additional information (Details) - USD ($)					1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 12, 2021	Jul. 24, 2020	Apr. 20, 2020	Jul. 09, 2019	Feb. 28, 2020	Jul. 22, 2019	Mar. 04, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jul. 14, 2021	Jun. 30, 2019	May 31, 2019	Jul. 26, 2018
Stockholders Equity [Line Items]
Number of preferred stock authorized								5,000,000		5,000,000			5,000,000			5,000,000
Number of common stock authorized								100,000,000		100,000,000			100,000,000			100,000,000	50,000,000
Number of shares issued										4,301,869
Aggregate registered amount for offerings															$ 150,000,000			$ 150,000,000
Average selling price								$ 6.53		$ 6.53
Net proceeds from issuance of stock										$ 27,200,000
Expenses incurred													$ 49,000
Number of option granted										1,987,480
Percentage of Milestone Activity Met by the Company										19.00%
Allocated share-based compensation expense								$ 999,000	$ 1,088,000	$ 3,224,000	$ 2,864,000
Exercise price per share								$ 8.12		$ 8.12
Expected life of the stock option										10 years
expected dividends										0.00%
Risk free interest rate, minimum										0.47%
Risk free rate maximum										1.12%
Total unrecognized compensation cost related to stock options								$ 5,665,000		$ 5,665,000
Amortized period										44 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares										860,650
Vesting period										4 years
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures								$ 236,106	328,841	$ 928,417	657,780
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number								6,864,854		6,864,854			5,165,204
Employees
Stockholders Equity [Line Items]
Number of option granted	1,323,400
Grant date fair value of unvested options										$ 7,042,000
Allocated share-based compensation expense								$ 124,000		338,000
Underwritten public offering
Stockholders Equity [Line Items]
Number of shares issued		6,052,631
Average selling price		$ 9.50
Gross Proceeds from issuance of stock		$ 57,500,000
Net proceeds from issuance of stock		$ 53,800,000
Restricted stock
Stockholders Equity [Line Items]
Vesting period													4 years
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures								45,000		131,000
March 4, 2019 Performance-Based Award | Restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross							22,220
Stock Issued During Period, Value, Restricted Stock Award, Gross							$ 179,000
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures								0	12,000	12,000	22,000
July 24,2020 Offering | Underwritten public offering
Stockholders Equity [Line Items]
Number of shares issued		6,052,631
Average selling price		$ 9.50
Gross Proceeds from issuance of stock		$ 57,500,000
Net proceeds from issuance of stock		$ 53,800,000
July 22, 2019 Performance-Based Award | Restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross						180,300
Stock Issued During Period, Value, Restricted Stock Award, Gross						$ 1,300,000
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures								54,000	256,000	259,000	461,000
February 28 2020 Performance Based Award | Restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross					168,100
Stock Issued During Period, Value, Restricted Stock Award, Gross					$ 1,014,000
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures								84,000	$ 84,000	443,000	$ 535,000
April 12, 2021 Performance Based Award | Restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross	235,765
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 2,220,000
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures								$ 177,000		$ 1,030,000
Jefferies LLC and B. Riley FBR, Inc
Stockholders Equity [Line Items]
Number of shares issued													4,110,625	191,244
aggregate offering price			$ 50,000,000	$ 25,000,000
Average selling price													$ 6.64	$ 4.11
Net proceeds from issuance of stock													$ 26,500,000	$ 762,000
Commission rate (as a percent)				3.00%
Exercise Price Ranging From 7.00 To 11.39 | Maximum
Stockholders Equity [Line Items]
Exercise price per share								$ 11.39		$ 11.39
Expected volatility										60.70%
Exercise Price Ranging From 7.00 To 11.39 | Minimum
Stockholders Equity [Line Items]
Exercise price per share								$ 7.00		$ 7.00
Expected volatility										59.90%
Subsequent event | Restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross												88,000
Stock Issued During Period, Value, Restricted Stock Award, Gross												$ 691,930
Subsequent event | Restricted stock | First 43,000 restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross												43,000
Subsequent event | Restricted stock | Second 43,000 restricted stock
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Gross												45,000
Subsequent event | Restricted stock | Second anniversary of the date of the grant | First 43,000 restricted stock
Stockholders Equity [Line Items]
Vesting percentage												33.00%
Subsequent event | Restricted stock | Third anniversary of the date of the grant | First 43,000 restricted stock
Stockholders Equity [Line Items]
Vesting percentage												33.00%
Subsequent event | Restricted stock | Fourth anniversary of the date of the grant | First 43,000 restricted stock
Stockholders Equity [Line Items]
Vesting percentage												33.00%