Note 5 - Revenue (Details Textual) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Contract with Customer, Asset, after Allowance for Credit Loss, Current, Total	$ 232,000		$ 0
Contract With Customer, Asset, Revenue Recognized	0		219,000
Contract with Customer, Liability, Total	0		0
Revenue, Remaining Performance Obligation, Amount	0		$ 13,000
Revenue from Contract with Customer, Including Assessed Tax	506,000	$ 2,902,000
Income Tax Expense (Benefit), Total	$ 38,000	153,000
Foreign Tax Authority [Member] | National Tax Agency, Japan [Member]
Royalty Withholding Tax	5.00%
Income Tax Expense (Benefit), Total	$ 25,000	140,000
Royalty [Member]
Revenue from Contract with Customer, Including Assessed Tax	$ 0	2,769,000
Royalty [Member] | Daiichi Sankyo Collaberation and License Agreement [Member]
Royalty Percentage	4.00%
Revenue from Contract with Customer, Including Assessed Tax	$ 0	2,769,000
Non Cash Royalty Revenue [Member]
Revenue from Contract with Customer, Including Assessed Tax	$ 493,000	$ 34,000