CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Balance sheet (Parenthetical)
Allowance for doubtful accounts	$ 249,513	$ 237,339
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600,000	600,000
Common stock, shares, issued	215,059	214,607
Treasury stock, shares	56,541	57,187