Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounts receivable, allowance	$ 7,959	$ 6,930
Treasury stock - Common stock, shares	55,597	50,035
Common Stock [Member]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	1,600,000	1,600,000
Common stock, shares issued	176,378	174,208
Common stock, shares outstanding	120,781	124,174
Class B Common Stock [Member]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000	400,000
Common stock, shares issued	12,800	12,800
Common stock, shares outstanding	12,800	12,800