MEZZANINE EQUITY, COMMON STOCK AND STOCKHOLDERS’ DEFICIT - SCHEDULE OF REDEEMABLE CONVERTIBLE PREFERRED STOCK (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Shares Authorized (in shares)	658,311,424	414,033,220	643,333,662
Shares issued (in shares)	412,742,897	412,742,897	321,626,778
Redeemable convertible preferred stock, outstanding (in shares)	412,742,897	412,742,897	321,626,778
Liquidation Amount	$ 2,191,086	$ 2,191,086	$ 922,786
Redeemable convertible preferred stock	$ 2,179,739	$ 2,179,739	$ 912,411
Series A
Temporary Equity [Line Items]
Shares Authorized (in shares)	131,913,460	131,913,460	263,826,920
Shares issued (in shares)	131,913,460	131,913,460	131,913,460
Redeemable convertible preferred stock, outstanding (in shares)	131,913,460	131,913,460	131,913,460
Per Share Liquidation Preference (in dollars per share)	$ 0.1954	$ 0.1954	$ 0.1954
Liquidation Amount	$ 25,777	$ 25,777	$ 25,777
Per Share Initial Conversion Price (in dollars per share)	$ 0.1954	$ 0.1954	$ 0.1954
Redeemable convertible preferred stock	$ 16,139	$ 16,139	$ 16,139
Series B
Temporary Equity [Line Items]
Shares Authorized (in shares)	80,263,020	80,263,020	160,526,040
Shares issued (in shares)	80,263,020	80,263,020	80,263,020
Redeemable convertible preferred stock, outstanding (in shares)	80,263,020	80,263,020	80,263,020
Per Share Liquidation Preference (in dollars per share)	$ 0.6354	$ 0.6354	$ 0.6354
Liquidation Amount	$ 50,999	$ 50,999	$ 50,999
Per Share Initial Conversion Price (in dollars per share)	$ 0.6354	$ 0.6354	$ 0.6354
Redeemable convertible preferred stock	$ 50,999	$ 50,999	$ 50,999
Series C
Temporary Equity [Line Items]
Shares Authorized (in shares)	43,788,180	43,788,180	87,576,360
Shares issued (in shares)	43,788,180	43,788,180	43,788,180
Redeemable convertible preferred stock, outstanding (in shares)	43,788,180	43,788,180	43,788,180
Per Share Liquidation Preference (in dollars per share)	$ 2.5121	$ 2.5121	$ 2.5121
Liquidation Amount	$ 110,000	$ 110,000	$ 110,000
Per Share Initial Conversion Price (in dollars per share)	$ 2.5121	$ 2.5121	$ 2.5121
Redeemable convertible preferred stock	$ 109,870	$ 109,870	$ 109,870
Series D
Temporary Equity [Line Items]
Shares Authorized (in shares)	35,774,761	35,774,761	71,549,522
Shares issued (in shares)	35,774,761	35,774,761	35,774,761
Redeemable convertible preferred stock, outstanding (in shares)	35,774,761	35,774,761	35,774,761
Per Share Liquidation Preference (in dollars per share)	$ 10.1450	$ 10.1450	$ 10.1450
Liquidation Amount	$ 362,935	$ 362,935	$ 362,935
Per Share Initial Conversion Price (in dollars per share)	$ 10.1450	$ 10.1450	$ 10.1450
Redeemable convertible preferred stock	$ 362,670	$ 362,670	$ 362,670
Series E
Temporary Equity [Line Items]
Shares Authorized (in shares)	29,887,357	29,887,357	59,854,820
Shares issued (in shares)	29,887,357	29,887,357	29,887,357
Redeemable convertible preferred stock, outstanding (in shares)	29,887,357	29,887,357	29,887,357
Per Share Liquidation Preference (in dollars per share)	$ 12.4827	$ 12.4827	$ 12.4827
Liquidation Amount	$ 373,075	$ 373,075	$ 373,075
Per Share Initial Conversion Price (in dollars per share)	$ 12.4827	$ 12.4827	$ 12.4827
Redeemable convertible preferred stock	$ 372,733	$ 372,733	$ 372,733
Series F
Temporary Equity [Line Items]
Shares Authorized (in shares)	48,000,000	48,000,000
Shares issued (in shares)	48,000,000	48,000,000
Redeemable convertible preferred stock, outstanding (in shares)	48,000,000	48,000,000
Per Share Liquidation Preference (in dollars per share)	$ 12.5000	$ 12.5000
Liquidation Amount	$ 600,000	$ 600,000
Per Share Initial Conversion Price (in dollars per share)	$ 12.5000	$ 12.5000
Redeemable convertible preferred stock	$ 599,284	$ 599,284
Series G
Temporary Equity [Line Items]
Shares Authorized (in shares)	44,406,442	44,406,442
Shares issued (in shares)	43,116,119	43,116,119
Redeemable convertible preferred stock, outstanding (in shares)	43,116,119	43,116,119
Per Share Liquidation Preference (in dollars per share)	$ 15.5000	$ 15.5000
Liquidation Amount	$ 668,300	$ 668,300
Per Share Initial Conversion Price (in dollars per share)	$ 15.5000	$ 15.5000
Redeemable convertible preferred stock	$ 668,044	$ 668,044

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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The aggregate liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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The per share liquidation preference (or restrictions) of stock classified as temporary equity that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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Amount to be paid per share that is classified as temporary equity by entity upon redemption. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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The maximum number of securities classified as temporary equity that are permitted to be issued by an entity's charter and bylaws. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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The number of securities classified as temporary equity that have been sold (or granted) to the entity's shareholders. Securities issued include securities outstanding and securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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The number of securities classified as temporary equity that have been issued and are held by the entity's shareholders. Securities outstanding equals securities issued minus securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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