Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Allowance for doubtful accounts	$ 228	$ 226
Common stock par value (in dollars per share)	$ 0.001	$ 0.001
Common stock authorized (in shares)	135,000,000	135,000,000
Common stock issued (in shares)	82,524,514	68,235,179
Common stock outstanding (in shares)	82,312,275	68,034,386
Treasury stock (in shares)	212,239	200,793
Convertible Preferred Stock
Convertible preferred stock par value (in dollars per share)	$ 0.001	$ 0.001
Convertible preferred stock authorized (in shares)	5,000,000	5,000,000
Convertible preferred stock issued (in shares)	0	0
Convertible preferred stock outstanding (in shares)	0	0

For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

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