OTHER CURRENT ASSETS - DETAIL OF OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
User-held fractional shares	$ 1,430,855	$ 802,483
Prepaid expenses	67,412	28,629
Securities owned	18,874	3,222
Other	25,761	16,804
Other current assets	$ 1,542,902	$ 851,138