Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 8,100	$ 8,673
Common stock - par value	$ 0.01	$ 0.01
Common stock - shares authorized	250,000,000	250,000,000
Common stock - shares issued	107,799,899	105,990,704
Treasury stock - shares at cost	48,697,852	42,845,444