Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 23,842	$ 22,416
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	119,771,155	118,206,262
Common stock, shares outstanding	91,662,043	82,471,770
Treasury stock, shares	28,109,112	35,734,492