Note 8 - Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2019

Notes Tables

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life		Aggregate Intrinsic Value
Outstanding at December 31, 2018		3,023,639		$	1.40
Forfeited		(114,301	)	$	1.11
Outstanding at March 31, 2019		2,909,338		$	1.41		9		--
Vested and expected to vest at March 31, 2019		1,911,105		$	1.73		8.8		--
Exercisable at March 31, 2019		876,955		$	2.79		7.9		--

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

	Number of Shares			Weighted-Average Exercise Price Per Share
Balance at December 31, 2018		17,265,208		$	2.99
Warrants expired		(83,420	)	$	56.20
Warrants exercised		(500,000	)	$	0.01
Outstanding at March 31, 2019		16,681,788		$	2.81
Exercisable at March 31, 2019		15,983,259		$	2.58