Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 25,236	$ 21,903
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	475,000,000	475,000,000
Common stock, shares issued (in shares)	120,911,444	120,539,041
Common stock, shares outstanding (in shares)	92,556,276	92,376,335
Treasury stock, shares (in shares)	28,355,168	28,162,706