Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Shareholders' equity
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Treasury Stock, Shares	41,523,470	40,719,438
Class A [Member]
Shareholders' equity
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	104,882,379	105,461,817
Class B [Member]
Shareholders' equity
Common stock, par value	$ 0	$ 0
Common stock, shares authorized	0	0
Common stock, shares issued	0	0