Note 14 - Commitments and Contingent Liabilities - Material Adverse Effect on Company's Financial Condition (Details) $ in Thousands	Mar. 31, 2021 USD ($)
Standby Letters of Credit [Member]
Total Amounts Committed	$ 171,156
Less Than 1 Year	144,733
1-3 Years	26,423
3-5 Years	0
Beyond 5 years	0
Standby Letters of Credit [Member] | Employee Related Commitment [Member]
Total Amounts Committed	79,476
Less Than 1 Year	53,053
1-3 Years	26,423
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	91,282
Less Than 1 Year	91,282
1-3 Years	0
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member]
Total Amounts Committed	626,099
Less Than 1 Year	582,368
1-3 Years	43,731
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Employee Related Commitment [Member]
Total Amounts Committed	83,524
Less Than 1 Year	71,024
1-3 Years	12,500
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Environmental Commitment [Member]
Total Amounts Committed	538,320
Less Than 1 Year	507,367
1-3 Years	30,953
3-5 Years	0
Beyond 5 years	0
Surety Bond [Member] | Other Commitment [Member]
Total Amounts Committed	4,255
Less Than 1 Year	3,977
1-3 Years	278
3-5 Years	0
Beyond 5 years	0
Other Guarantee Obligations [Member] | Other Commitment [Member]
Total Amounts Committed	7,306
Less Than 1 Year	6,377
1-3 Years	398
3-5 Years	398
Beyond 5 years	$ 133