Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 7,017	$ 8,100
Common stock - par value	$ 0.01	$ 0.01
Common stock - shares authorized	250,000,000	250,000,000
Common stock - shares issued	108,187,035	107,799,899
Treasury stock - shares at cost	49,186,583	48,697,852