Note 13 - Commitments and Contingent Liabilities - Material Adverse Effect on Company's Financial Condition (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Total Amounts Committed	$ 748,240
Less Than 1 Year	719,007
1-3 Years	28,553
3-5 Years	398
Beyond 5 years	282
Standby Letters of Credit [Member]
Total Amounts Committed	109,426
Less Than 1 Year	89,901
1-3 Years	19,525
3-5 Years	0
Beyond 5 years	0
Standby Letters of Credit [Member] | Employee Related Commitment [Member]
Total Amounts Committed	68,346
Less Than 1 Year	50,925
1-3 Years	17,421
3-5 Years	0
Beyond 5 years	0
Standby Letters of Credit [Member] | Environmental Commitment [Member]
Total Amounts Committed	398
Less Than 1 Year	398
1-3 Years	0
3-5 Years	0
Beyond 5 years	0
Standby Letters of Credit [Member] | Other Commitment [Member]
Total Amounts Committed	40,682
Less Than 1 Year	38,578
1-3 Years	2,104
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member]
Total Amounts Committed	626,710
Less Than 1 Year	622,373
1-3 Years	4,337
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Employee Related Commitment [Member]
Total Amounts Committed	87,424
Less Than 1 Year	87,424
1-3 Years	0
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Environmental Commitment [Member]
Total Amounts Committed	535,155
Less Than 1 Year	531,461
1-3 Years	3,694
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Other Commitment [Member]
Total Amounts Committed	4,131
Less Than 1 Year	3,488
1-3 Years	643
3-5 Years	0
Beyond 5 years	0
Other Guarantee Obligations [Member]
Total Amounts Committed	12,104
Less Than 1 Year	6,733
1-3 Years	4,691
3-5 Years	398
Other Guarantee Obligations [Member] | Other Commitment [Member]
Total Amounts Committed	12,104
Less Than 1 Year	6,733
1-3 Years	4,691
3-5 Years	398
Beyond 5 years	$ 282