Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets:
Accounts receivable, allowances for doubtful accounts	$ 2,005	$ 7,187
Stockholders' equity
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized (in shares)	1,000,000	1,000,000
Preferred stock, shares issued	0	0
Common Stock [Member]
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares outstanding (in shares)	143,735,481	150,611,657
Class B Convertible Common Stock [Member]
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, shares outstanding (in shares)	13,452,549	14,352,839