CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounts receivable, allowance for doubtful accounts	$ 18,905	$ 10,845
Intangible assets, accumulated amortization	$ 42,050	$ 28,394
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	84,696,227	85,242,387
Common stock, outstanding	84,696,227	85,242,387