Note 9 - Fair Values - Quantitative Information about Level 3 Fair Value Measurements (Details) - Fair Value, Inputs, Level 3 [Member]	Sep. 30, 2020
Minimum [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	0
Minimum [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	0
Minimum [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	0
Minimum [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	0.01
Maximum [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	1
Maximum [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	0.7742
Maximum [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	0.3447
Maximum [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	0.104
Weighted Average [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	(0.0254)
Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	(0.1593)
Weighted Average [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	(0.1795)
Weighted Average [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	(0.0399)