Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010
Consolidated Balance Sheets
Accounts receivable, allowance for doubtful accounts	$ 16,345	$ 14,256
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	112,132,551	111,522,354
Common stock, shares outstanding	80,250,881	79,655,213
Treasury stock, shares	31,881,670	31,867,141