CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 17,918	$ 19,443
Intangible assets, accumulated amortization	$ 74,676	$ 64,215
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	85,920,543	85,987,883
Common stock, outstanding	85,920,543	85,987,883