SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Operating items, net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Other operating items, net	$ 754	$ 1,305
Professional service fees	600	100
Equipment, supplies and employee testing expenses due to the COVID-19 pandemic	$ 100
Pre-opening expenses relating to the Monarch Black Hawk Expansion project		800
Colorado legislation lobbying expenses		$ 400