Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 47,779	$ 32,506
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)	121,837,990	121,259,960
Common stock, shares outstanding (in shares)	89,558,913	91,836,938
Treasury stock, shares (in shares)	32,279,077	29,423,022