Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 21,903	$ 23,842
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000,000	475,000,000
Common stock, shares issued	120,539,041	119,771,155
Common stock, shares outstanding	92,376,334	91,662,043
Treasury stock, shares	28,162,706	28,109,112