ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Loyalty Program Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Movement in Deferred Revenue [Roll Forward]
Loyalty program deferred revenue, beginning balance	$ 7,033	$ 8,073
Loyalty points forfeited or expired	(5,895)	(6,963)
Loyalty points used	(14,316)	(15,451)
Loyalty points vested	17,836	20,085
Loyalty points unvested	1,748	1,289
Loyalty program deferred revenue, ending balance	$ 6,406	$ 7,033