Note 4 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	$ 61,812	$ 57
Fair Value, Nonrecurring [Member]
Loans Receivable, Fair Value Disclosure	100	1,300
Collateralized Loan Obligations [Member]
Other than Temporary Impairment Losses, Investments, Total	4,200	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	10,300	$ 9,400
Fair Value, Inputs, Level 3 [Member] | Collateralized Loan Obligations [Member]
Other than Temporary Impairment Losses, Investments, Total	$ 4,200