Note 9 - Fair Values - Quantitative Information about Level 3 Fair Value Measurements (Details) - Fair Value, Inputs, Level 3 [Member]	Mar. 31, 2020
Minimum [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	0.51
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	3.33
Maximum [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	100
Maximum [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	77.42
Maximum [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	34.47
Maximum [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	9.08
Weighted Average [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	1.72
Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	18.72
Weighted Average [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	20.79
Weighted Average [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	4.82