ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loyalty Deferred Revenue (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Loyalty program
Loyalty deferred revenue, beginning balance	$ 4,487	$ 3,127
Loyalty points forfeited or expired	(2,108)	(3,249)
Loyalty points used	(4,735)	(9,385)
Loyalty points vested	5,333	12,771
Loyalty points unvested	1,194	1,223
Loyalty deferred revenue, ending balance	4,171	4,487
Deferred commissions	$ 2,338	$ 2,343