Consolidated Balance Sheets (Parentheticals) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Class A Common Stock [Member]
Common Stock, Par Value Per Share	$ 0.01	$ 0.01
Common Stock, Voting Rights	1	1
Common Stock, Shares Authorized	180,000,000	180,000,000
Common Stock, Shares, Issued	74,808,305	74,162,972
Common Stock, Shares, Outstanding	61,946,078	61,362,665
Treasury Stock, Shares	12,862,227	12,800,307
Class B Common Stock [Member]
Common Stock, Par Value Per Share	$ 0.01	$ 0.01
Common Stock, Voting Rights	10	10
Common Stock, Shares Authorized	30,000,000	30,000,000
Common Stock, Shares, Issued	701,138	758,138
Common Stock, Shares, Outstanding	701,138	758,138