Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Stockholders' Equity :
Convertible preferred stock, shares issued
Treasury stock, shares	15,647,234	14,980,640
Common Class A
Stockholders' Equity :
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	56,307,273	55,738,639
Common stock, shares outstanding	40,660,039	40,757,999
Common Class B
Stockholders' Equity :
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares outstanding	12,029,375	12,029,375