CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 18,687	$ 19,134
Intangible assets, accumulated amortization	$ 95,451	$ 88,098
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	85,008,833	85,500,037
Common stock, outstanding	85,008,833	85,500,037