ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loyalty Deferred Revenue (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Loyalty program
Loyalty deferred revenue, beginning balance	$ 3,127	$ 4,231
Loyalty points forfeited or expired	(1,659)	(4,348)
Loyalty points used	(4,649)	(9,127)
Loyalty points vested	5,124	11,320
Loyalty points unvested	1,121	1,051
Loyalty deferred revenue, ending balance	3,064	3,127
Deferred commissions	$ 1,650	$ 1,758