Note 9 - Fair Value Disclosures - Quantitative Information About Level 3 Fair Value Measurements (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Total other investments, at fair value	$ 58,540	$ 14,864
Collateralized Loan Obligations [Member]
Total other investments, at fair value		2,522
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Yield Rate [Member]
Total other investments, at fair value		$ 2,522
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Yield Rate [Member] | Weighted Average [Member]
Other investments, measurement		0.179
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Yield Rate [Member] | Minimum [Member]
Other investments, measurement		0.169
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Yield Rate [Member] | Maximum [Member]
Other investments, measurement		0.192
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Expected Term [Member] | Weighted Average [Member]
Other investments, measurement		0.058
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Expected Term [Member] | Minimum [Member]
Other investments, measurement		0.053
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Expected Term [Member] | Maximum [Member]
Other investments, measurement		0.065
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Default Rate [Member] | Weighted Average [Member]
Other investments, measurement		0.02
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Default Rate [Member] | Minimum [Member]
Other investments, measurement		0.02
Collateralized Loan Obligations [Member] | Valuation Technique, Discounted Cash Flow [Member] | Fair Value, Inputs, Level 3 [Member] | Measurement Input, Default Rate [Member] | Maximum [Member]
Other investments, measurement		0.02