Note 14 - Commitments and Contingent Liabilities - Material Adverse Effect on Company's Financial Condition (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Total Amounts Committed	$ 807,327
Less Than 1 Year	717,875
1-3 Years	88,822
3-5 Years	398
Beyond 5 years	232
Standby Letters of Credit [Member]
Total Amounts Committed	129,226
Less Than 1 Year	100,831
1-3 Years	28,395
3-5 Years	0
Beyond 5 years	0
Standby Letters of Credit [Member] | Employee Related Commitment [Member]
Total Amounts Committed	75,846
Less Than 1 Year	52,929
1-3 Years	22,917
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	52,982
Less Than 1 Year	47,504
1-3 Years	5,478
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member]
Total Amounts Committed	667,397
Less Than 1 Year	610,408
1-3 Years	56,989
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Employee Related Commitment [Member]
Total Amounts Committed	86,024
Less Than 1 Year	50,524
1-3 Years	35,500
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Environmental Commitment [Member]
Total Amounts Committed	576,584
Less Than 1 Year	555,300
1-3 Years	21,284
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Other Commitment [Member]
Total Amounts Committed	4,789
Less Than 1 Year	4,584
1-3 Years	205
3-5 Years	0
Beyond 5 years	0
Other Guarantee Obligations [Member]
Total Amounts Committed	10,704
Less Than 1 Year	6,636
1-3 Years	3,438
3-5 Years	398
Other Guarantee Obligations [Member] | Other Commitment [Member]
Total Amounts Committed	10,704
Less Than 1 Year	6,636
1-3 Years	3,438
3-5 Years	398
Beyond 5 years	$ 232