Consolidated Balance Sheets Parentheticals - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Class A Common Shares [Member]
Common Stock, par value per share	$ 0.01	$ 0.01
Common Stock, votes per share	1	1
Common Stock, shares authorized	180,000,000	180,000,000
Common Stock, shares issued	75,199,229	74,808,305
Common Stock, shares outstanding	58,737,895	61,946,078
Treasury Stock, shares	16,461,334	12,862,227
Class B Common Shares [Member]
Common Stock, par value per share	$ 0.01	$ 0.01
Common Stock, votes per share	10	10
Common Stock, shares authorized	30,000,000	30,000,000
Common Stock, shares issued	541,138	701,138
Common Stock, shares outstanding	541,138	701,138