SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Operating items, net (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Other operating items, net	$ 812	$ 1,157	$ 1,566	$ 2,462
Professional service fees		200	1,500	300
Equipment, supplies and employee testing expenses due to the COVID-19 pandemic		300	$ 100	300
Pre-opening expenses relating to the Monarch Black Hawk Expansion project		200		1,000
Colorado legislation lobbying expenses		$ 500		$ 900