ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loyalty Deferred Revenue (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Loyalty program
Loyalty deferred revenue, beginning balance	$ 4,231	$ 6,406
Loyalty points forfeited or expired	(3,487)	(4,332)
Loyalty points used	(6,720)	(11,398)
Loyalty points vested	8,441	12,469
Loyalty points unvested	1,114	1,086
Loyalty deferred revenue, ending balance	$ 3,579	$ 4,231