SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Customer Concentration (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Concentration Risk [Line Items]
Net revenues	$ 82,411	$ 69,528	$ 240,290	$ 195,833
Accounts receivable, net of allowance for doubtful accounts of $275 and $610 as of September 30, 2021, and December 31, 2020, respectively	46,798		46,798		$ 50,589
Revenue Benchmark | Customer Concentration Risk | Customer A
Concentration Risk [Line Items]
Net revenues	$ 15,409	$ 13,479	$ 41,594	$ 33,547
Concentration risk, percentage	18.70%	19.40%	17.30%	17.10%
Revenue Benchmark | Customer Concentration Risk | Customer B
Concentration Risk [Line Items]
Net revenues	$ 13,492	$ 12,215	$ 44,888	$ 34,636
Concentration risk, percentage	16.40%	17.60%	18.70%	17.70%
Accounts Receivable | Customer Concentration Risk | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage			9.30%		15.00%
Accounts receivable, net of allowance for doubtful accounts of $275 and $610 as of September 30, 2021, and December 31, 2020, respectively	$ 4,344		$ 4,344		$ 7,582
Accounts Receivable | Customer Concentration Risk | Customer B
Concentration Risk [Line Items]
Concentration risk, percentage			16.20%		6.80%
Accounts receivable, net of allowance for doubtful accounts of $275 and $610 as of September 30, 2021, and December 31, 2020, respectively	$ 7,558		$ 7,558		$ 3,447