Note 9 - Fair Values - Quantitative Information about Level 3 Fair Value Measurements (Details) - Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2021
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	0.7553
Maximum [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	0.2777
Maximum [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	0.0883
Weighted Average [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	0.0243
Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	0.1224
Weighted Average [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	0.1071
Weighted Average [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	0.0391