CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Convertible preferred stock issued	0	0
Common Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	62,586,381	62,046,966
Common stock, shares outstanding	37,910,938	38,890,533
Treasury stock, shares	24,675,443	23,156,433
Common Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	12,029,375	12,029,375
Common stock, shares outstanding	12,029,375	12,029,375