CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Accounts receivable, allowance	$ 264,144	$ 242,674
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, issued	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	450,000,000	450,000,000
Common stock, shares issued	217,120,346	215,640,968
Common stock, shares outstanding	209,754,247	215,640,968
Treasury stock, shares	7,366,099