CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accounts receivable, allowance for doubtful accounts	$ 20,204	$ 19,443
Intangible assets, accumulated amortization	$ 68,932	$ 64,215
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	86,218,005	85,987,883
Common stock, outstanding	86,218,005	85,987,883