Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer, Including Assessed Tax		$ 5,613	$ 5,317	$ 19,860	$ 12,384
Retained Earnings (Accumulated Deficit), Ending Balance		(666,485)		(666,485)		$ (609,208)
Cash and Cash Equivalents, at Carrying Value, Ending Balance		64,493	148,851	64,493	148,851	137,686	$ 90,642
Cash and Cash Equivalents, Period Increase (Decrease), Total				(73,200)
Accounts Receivable, after Allowance for Credit Loss, Current, Total		6,174		6,174		3,803
Restricted Cash and Cash Equivalents, Noncurrent, Total		3,327	1,529	3,327	1,529	1,534	$ 1,522
Operating Lease, Right-of-Use Asset		13,681		13,681		0
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance		3,470		3,470		2,698
Operating Lease, Liability, Total		15,726		15,726		$ 0
Transfer Agreement of Bone Scan Index Product Rights for Use in Japan [Member] | FUJIFILM [Member]
Proceeds From Sale of License				4,000
Product [Member]
Revenue from Contract with Customer, Including Assessed Tax		570		840
License and Other [Member]
Revenue from Contract with Customer, Including Assessed Tax		$ 131	$ 148	$ 6,354	$ 627
License and Other [Member] | Milestone Payment for Bayer Phase 1 Trial [Member]
Revenue from Contract with Customer, Including Assessed Tax	$ 2,000