Note 2 - Acquisitions and Divestitures - Schedule of Business Acquisition Assets and Liabilities of Valley Forge Convention Center Partners (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Sep. 17, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill	$ 1,083,287	$ 1,062,102		$ 888,224	$ 826,476
Valley Forge Convention Center Partners, L.P. [Member]
Current assets	29,280
Property and equipment	57,118
Other assets	2,872
Intangible assets	136,600
Total acquired assets	225,870
Current liabilities	12,968
Other liabilities	9,803
Total liabilities assumed	22,771
Net identifiable assets acquired	203,099
Goodwill	85,966
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net, Total	289,065		$ 289,100
Previously Reported [Member] | Valley Forge Convention Center Partners, L.P. [Member]
Current assets		29,909
Property and equipment		56,500
Other assets		483
Intangible assets		148,600
Total acquired assets		235,492
Current liabilities		12,968
Other liabilities		606
Total liabilities assumed		13,574
Net identifiable assets acquired		221,918
Goodwill		69,446
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net, Total		$ 291,364
Restatement Adjustment [Member] | Valley Forge Convention Center Partners, L.P. [Member]
Current assets	(629)
Property and equipment	618
Other assets	2,389
Intangible assets	(12,000)
Total acquired assets	(9,622)
Current liabilities	0
Other liabilities	9,197
Total liabilities assumed	9,197
Net identifiable assets acquired	(18,819)
Goodwill	16,520
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net, Total	$ (2,299)