Consolidated Balance Sheets Parentheticals - $ / shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
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	75,696,850		75,240,513
Common Stock, shares outstanding	56,663,012		56,349,327
Treasury Stock, shares	19,033,838		18,891,186
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	376,392		517,138
Common Stock, shares outstanding	376,392		517,138