Note 2 - Acquisitions and Divestitures - Business Acquisition Income Statement Supplemental Information of Valley Forge Convention Center Partners (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 24,296	$ 39,405	$ 48,484	$ 45,451	$ 22,867		$ 11,837	$ 38,945	$ 41,399	$ 157,636	$ 115,048	$ 189,390
Valley Forge Convention Center Partners, L.P. [Member]
Total revenues						$ 43,499				168,610
Net income						$ 4,450				$ 31,286