Note 10 - Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income tax benefit using U.S. federal statutory rate	$ (9,696)	$ (7,315)	$ (1,136)
Permanent differences	430	260	124
Orphan Drug credit permanent addback	1,437	1,310	674
State income taxes, net of federal benefit	(498)	(808)	(303)
Tax credits	(4,846)	(4,219)	(2,176)
Expired net operating losses and tax credits			312
Change in valuation allowance	8,804	9,782	4,394
Mark-to-market derivative liability			(1,779)
Foreign rate differential	4,304
Other	$ 65	$ 990	$ (110)