Note 9 - Fair Values - Quantitative Information about Level 3 Fair Value Measurements (Details) - Fair Value, Inputs, Level 3 [Member]	Jun. 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	1
Maximum [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	1.0
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	0.1173
Weighted Average [Member] | Measurement Input, Default Rate [Member]
Significant unobservable input	0.0163
Weighted Average [Member] | Measurement Input, Loss Severity [Member]
Significant unobservable input	0.1598
Weighted Average [Member] | Measurement Input, Prepayment Rate [Member]
Significant unobservable input	0.1791
Weighted Average [Member] | Measurement Input, Discount Rate [Member]
Significant unobservable input	0.0413