Note 8 - Fair Value Disclosures - Level 3 Rollforward (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Beginning of period		$ 0	$ 4,833	$ 0	$ 2,522
Net trading		0	37	0	(41)
Gains & losses (1)	[1]	0	(58)	0	(661)
Accretion of income (1)	[1]	0	46	0	124
Purchases		0	29	0	638
Sales and returns of capital		0	(2,565)	0	(5,538)
Reclassification of RTLs		0	0	0	5,278
End of period		0	2,322	0	2,322
Change in unrealized gains / (losses) (2)	[2]	$ 0	$ 0	$ 0	$ 0

[1] Gains and losses and accretion of income on other investments, at fair value are recorded as a component of principal transactions and other income in the consolidated statements of operations.

[2] Represents the change in unrealized gains and losses for the period included in earnings for assets held at the end of the reporting period.