Note 6 - Note Payable - Summary of Note Payable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	[1]
2018 (remaining nine months)	$ 2,020
2019	2,778
2020	2,901
2021	16,672
2022	19,306
Thereafter	6,221
Total payments	49,898
Less: Amount representing interest	(19,098)
Present value of obligations	30,800
Less: Unamortized debt discount	(1,466)
Note payable, noncurrent portion	$ 29,334	$ 28,948

[1] The condensed consolidated balance sheet as of December 31, 2017 has been derived from the audited consolidated financial statements as of that date.