SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Operating items, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Other operating items, net	$ 4,929	$ 6,711	$ 3,112
Professional service fees	5,100	1,600
Loss on disposition of assets	100
Litigation proceeds	300
Insurance claim proceeds	100
Pre-opening expenses relating to the Monarch Black Hawk Expansion project		2,800
Colorado legislation lobbying expenses		1,400
Equipment, supplies and employee testing expenses due to the COVID-19 pandemic	$ 100	700
Write off of Deferred Debt Issuance Cost		95
Unamortized debt issuance cost write off and loss on disposal of assets		$ 200