Note 10 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Notes Tables

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

	Year Ended December 31,
	2015			2014			2013
Income tax benefit using U.S. federal statutory rate	$	(7,315	)	$	(1,136	)	$	(2,690	)
Permanent differences		260			124			299
Orphan Drug credit permanent addback		1,310			674			-
State income taxes, net of federal benefit		(808	)		(303	)		(389	)
Tax credits		(4,219	)		(2,176	)		(7,164	)
Expired net operating losses and tax credits		-			312			2,566
Change in valuation allowance		9,782			4,394			7,286
Mark-to-market derivative liability		-			(1,779	)		-
Other		990			(110	)		92
	$	-		$	-		$	-

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

	Year Ended December 31,
	2015			2014			2013
Net operating loss carryforwards	$	34,488		$	29,217		$	26,304
Federal and state tax credits		16,404			12,126			9,941
Deferred revenue		-			-			1,147
Accrued expenses		27			478			332
Patents		443			531			612
Stock-based compensation		596			92
Other		276			8			300
		52,234			42,452			38,636
Valuation allowance		(52,234	)		(42,452	)		(38,636	)
Net deferred tax asset	$	-		$	-		$	-