Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,703	$ 1,266
Preferred stock, par value (usd per share)	$ 0.001	$ 0.001
Preferred stock, number of shares authorized (in shares)	40,000,000	40,000,000
Preferred stock, number of shares outstanding (in shares)	0	0
Common stock, par value (usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	1,460,000,000	1,460,000,000
Common stock, number of shares issued (in shares)	728,558,989	774,293,197
Common stock, number of shares outstanding (in shares)	728,558,989	774,293,197

The valuation allowance as of the balance sheet date to reduce the gross amount of receivables to estimated net realizable value, which would be presented in parentheses on the face of the balance sheet.

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