SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Change in Accounting Estimate (Details)	1 Months Ended	3 Months Ended								12 Months Ended			15 Months Ended	18 Months Ended
	Oct. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) item $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Change in Accounting Estimate
Net book value		$ 214,899,000				$ 203,154,000				$ 214,899,000	$ 203,154,000			$ 203,154,000
Depreciation expense per month													$ 300,000
Depreciation expense net of tax per month													$ 200,000
Net income		6,470,000	$ 7,834,000	$ 5,695,000	$ 4,575,000	5,123,000	$ 6,394,000	$ 5,099,000	$ 4,043,000	$ 24,574,000	20,659,000	$ 14,185,000
SEGMENT INFORMATION
Number of reportable segments | item										1
Monarch Black Hawk Parking Structure
Change in Accounting Estimate
Net book value		$ 4,800,000								$ 4,800,000
Estimated depreciable life										P37Y
Monarch Black Hawk Parking Structure | Service Life
Change in Accounting Estimate
Net book value						$ 2,900,000	$ 400,000				2,900,000			$ 2,900,000
Estimated depreciable life													P15M	P18M
Depreciation expense net of tax per month	$ 40,000
Depreciation expense										$ 300,000.00	1,400,000	2,900,000
Net income										$ (200,000.00)	$ (900,000)	$ (1,900,000)
Basic and diluted earnings per share (in dollars per share) | $ / shares										$ (0.01)	$ 0.05	$ (0.11)