CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts	$ 19,443	$ 18,905
Intangible assets, accumulated amortization	$ 64,215	$ 42,050
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	85,987,883	84,696,227
Common stock, outstanding	85,987,883	84,696,227