Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts	$ 19,995	$ 15,315
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	116,266,406	113,741,883
Common stock, shares outstanding	84,384,736	81,860,213
Treasury stock ,shares	31,881,670	31,881,670