Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Accounts receivable, allowance for doubtful accounts	$ 68	$ 68	$ 26	$ 0	$ 0	$ 0	$ 0	$ 6
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Common stock, authorized (in shares)	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000
Common stock, issued (in shares)	20,825,452	20,344,825	18,898,609	18,717,095	18,547,406	18,237,425	16,107,505	14,145,413
Common stock, outstanding (in shares)	20,825,452	20,344,825	18,898,609	18,717,095	18,547,406	18,237,425	16,107,505	14,145,413

Amount of allowance for credit loss on accounts receivable, classified as current.

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