Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6,917	$ 8,100
Common stock - par value	$ 0.01	$ 0.01
Common stock - shares authorized	250,000,000	250,000,000
Common stock - shares issued	108,530,911	107,799,899
Treasury stock - shares at cost	50,495,378	48,697,852