Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 15,950	$ 18,228
Preferred Stock, Par value per share (in dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares authorized	100,000,000	100,000,000
Preferred Stock, Shares issued	0	0
Preferred Stock, Shares outstanding	0	0
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 issued	81,119,117	79,440,404
Common Stock, Shares outstanding	80,722,258	79,038,062
Treasury stock, at cost (shares)	396,859	402,342

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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