Condensed Consolidated Balance Sheets - Parenthetical - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 18,212	$ 15,950
Common Stock, Par value per share (in dollars per share)	$ 0.001	$ 0.001
Common Stock, Shares authorized	300,000,000	300,000,000
Common Stock, Shares outstanding	84,070,003	80,722,258
Treasury stock, at cost (shares)	395,153	396,859