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CONVERTIBLE PREFERRED STOCK - Schedule of Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Authorized (in shares)	19,074		19,074
Outstanding (in shares)	19,074	19,074	19,074	18,488	18,247	18,247
Aggregate liquidation preference	$ 183,300		$ 183,300
Funds received	183,300		183,300
Fees incurred	691		691
Carrying value of convertible preferred stock	$ 182,609	$ 182,609	$ 182,609	$ 147,662	$ 137,686	$ 137,686
Series A Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	3,865		3,865
Outstanding (in shares)	3,865		3,865
Per share price at issuance (in usd per share)	$ 0.85		$ 0.85
Aggregate liquidation preference	$ 3,300		$ 3,300
Funds received	3,300		3,300
Fees incurred	52		52
Carrying value of convertible preferred stock	$ 3,248		$ 3,248
Series B Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	6,298		6,298
Outstanding (in shares)	6,298		6,298
Per share price at issuance (in usd per share)	$ 2.38		$ 2.38
Aggregate liquidation preference	$ 15,000		$ 15,000
Funds received	15,000		15,000
Fees incurred	60		60
Carrying value of convertible preferred stock	$ 14,940		$ 14,940
Series C Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	2,948		2,948
Outstanding (in shares)	2,948		2,948
Per share price at issuance (in usd per share)	$ 6.78		$ 6.78
Aggregate liquidation preference	$ 20,000		$ 20,000
Funds received	20,000		20,000
Fees incurred	112		112
Carrying value of convertible preferred stock	$ 19,888		$ 19,888
Series D Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	3,154		3,154
Outstanding (in shares)	3,154		3,154
Per share price at issuance (in usd per share)	$ 14.27
Aggregate liquidation preference	$ 45,000		$ 45,000
Funds received	45,000		45,000
Fees incurred	146		146
Carrying value of convertible preferred stock	$ 44,853		$ 44,853
Series E Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	1,224		1,224
Outstanding (in shares)	1,224		1,224
Per share price at issuance (in usd per share)	$ 20.43		$ 20.43
Aggregate liquidation preference	$ 25,000		$ 25,000
Funds received	25,000		25,000
Fees incurred	92		92
Carrying value of convertible preferred stock	$ 24,909		$ 24,909
Series F Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	758
Outstanding (in shares)	758		758
Per share price at issuance (in usd per share)	$ 39.57		$ 39.57
Aggregate liquidation preference	$ 30,000		$ 30,000
Funds received	30,000		30,000
Fees incurred	153		153
Carrying value of convertible preferred stock	$ 29,848		$ 29,848
Series G Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	241		241
Outstanding (in shares)	241		241
Per share price at issuance (in usd per share)	$ 41.38		$ 41.38
Aggregate liquidation preference	$ 10,000		$ 10,000
Funds received	10,000		10,000
Fees incurred	24		24
Carrying value of convertible preferred stock	$ 9,976		$ 9,976
Series H Preferred Stock
Temporary Equity [Line Items]
Authorized (in shares)	586		586
Outstanding (in shares)	586		586
Per share price at issuance (in usd per share)	$ 59.77		$ 59.77
Aggregate liquidation preference	$ 35,000		$ 35,000
Funds received	35,000		35,000
Fees incurred	52		52
Carrying value of convertible preferred stock	$ 34,947		$ 34,947

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