SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Change in Accounting Estimate (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended	15 Months Ended	18 Months Ended
	Oct. 31, 2015 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($) $ / shares	Jun. 30, 2017 USD ($) item	Jun. 30, 2016 USD ($) $ / shares	Dec. 31, 2013 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)
Debt Issuance Costs
Loan issuance costs, net of amortization		$ 2,200		$ 2,200
Change in Accounting Estimate
Net book value		228,049		228,049					$ 214,899
Net income		$ 7,239	$ 5,695	$ 12,111	$ 10,270
SEGMENT INFORMATION
Number of operating segments | item				2
Number of reportable segments | item				1
Monarch Black Hawk Parking Structure
Change in Accounting Estimate
Net book value						$ 4,800
Estimated depreciable life						P37Y
Monarch Black Hawk Parking Structure | Service Life
Change in Accounting Estimate
Net book value								$ 2,900		$ 400
Estimated depreciable life							P15M	P18M
Depreciation expense per month							$ 300
Depreciation expense net of tax per month							$ 200
Depreciation expense	$ 40		133		266
Net income			$ 87		$ (173)
Basic and diluted earnings per share (in dollars per share) | $ / shares			$ 0.01		$ 0.01