Note 11 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]

	Year Ended December 31,
	2017			2016			2015
Domestic	$	(24,803	)	$	(15,860	)	$	(21,377	)
Foreign		(5,161	)		(12,666	)		-
Loss before income taxes	$	(29,964	)	$	(28,526	)	$	(21,377	)

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	Year Ended December 31,
	2017			2016			2015
Income tax benefit using U.S. federal statutory rate	$	(10,186	)	$	(9,696	)	$	(7,315	)
Permanent differences		4			430			260
Stock Compensation - Perm Items		689			-			-
R&D Credit -Perm Items		1,751			1,437			1,310
State income taxes, net of federal benefit		(853	)		(498	)		(808	)
Tax credits		(5,495	)		(4,846	)		(4,219	)
Change in valuation allowance		(54,319	)		8,804			9,782
Foreign rate differential		1,752			4,304			-
Rate change		2,202			-			-
382 Limitation		64,975			-			-
Other		(520	)		65			990
	$	-		$	-		$	-

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	Year Ended December 31,
	2017			2015			2014
Net operating loss carryforwards	$	2,651		$	42,156		$	34,488
Federal and state tax credits		2,244			21,223			16,404
Accrued expenses		399			544			27
Patents		191			360			443
Stock-based compensation		1,262			1,353			596
Other		202			320			276
		6,949			65,956			52,234
Valuation allowance		(6,949	)		(65,956	)		(52,234	)
Net deferred tax asset	$	-		$	-		$	-