ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loyalty Program Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Movement in Deferred Revenue [Roll Forward]
Loyalty program deferred revenue, beginning balance	$ 6,406	$ 7,033
Loyalty points forfeited or expired	(4,332)	(5,895)
Loyalty points used	(11,398)	(14,316)
Loyalty points vested	12,469	17,836
Loyalty points unvested	1,086	1,748
Loyalty program deferred revenue, ending balance	$ 4,231	$ 6,406