ACQUISITION, INTEGRATION AND RESTRUCTURING EXPENSE - Restructuring Charges (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Acquisition costs for other recently announced and pending acquisitions	$ 10,900,000	$ 6,844,000
Restructuring expense	1,268,000	0
Total acquisition, integration and restructuring expense	12,168,000	6,844,000	$ 0
Dover Downs Merger
Restructuring Cost and Reserve [Line Items]
Acquisition costs for other recently announced and pending acquisitions	7,883,000	6,636,000
Black Hawk, CO Properties
Restructuring Cost and Reserve [Line Items]
Acquisition costs for other recently announced and pending acquisitions	1,724,000	208,000
Other Recently Announced and Pending Acquisitions
Restructuring Cost and Reserve [Line Items]
Acquisition costs for other recently announced and pending acquisitions	$ 1,293,000	$ 0