Note 10 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Common Stock, Shares Authorized		160,000,000		160,000,000
Common Stock, Par or Stated Value Per Share		$ 0.0013		$ 0.0013
Preferred Stock, Shares Authorized		20,000,000		20,000,000
Preferred Stock, Par or Stated Value Per Share		$ 0.001		$ 0.001
Replacement Shelf Registration			$ 250,000
Common Stock Sales Agreement with Agent, Maximum Aggregate Offering Price	$ 75,000
Stock Issued During Period, Shares, New Issues		1,537,528
Stock Issued During Period, Value, New Issues		$ 9,525
Sale of Stock, Price Per Share		$ 6.33
Common Stock, Shares Subscribed but Unissued		103,100
Common Stock, Share Subscribed but Unissued, Subscriptions Receivable		$ 750		$ 2,109
Sale of Subscribed Common Stock, Price Per Share		$ 7.50
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		$ 0	$ 0