CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 10,135	$ 8,602
Common stock, par value (in USD per share)	$ 0.000001	$ 0.000001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	83,956,890	83,724,916
Common stock, shares outstanding (in shares)	83,596,510	83,724,916