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Note 10 - Retirement Plans - Fair Value of Plan Assets (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Mar. 31, 2021 | Mar. 31, 2020
--- | --- | --- | ---
Plan Assets, Amount |  | $ 327,867 | $ 348,914 | $ 202,485
Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Plan Assets, Amount |  | 29,427 |  |
Defined Benefit Plan, Equity Securities Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 40,969 |  |
Defined Benefit Plan, Real Estate Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 23,200 |  |
Defined Benefit Plan, Debt Security Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 200,225 |  |
Defined Benefit Plan, Cash and Short-term Investments Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [1] | 22,224 |  |
Other Investments [Member] |  |  |  |
Plan Assets, Amount |  | 11,822 |  |
Fair Value, Inputs, Level 1 [Member] |  |  |  |
Plan Assets, Amount |  | 29,427 |  |
Fair Value, Inputs, Level 1 [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Plan Assets, Amount |  | 29,427 |  |
Fair Value, Inputs, Level 1 [Member] | Defined Benefit Plan, Equity Securities Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1 [Member] | Defined Benefit Plan, Real Estate Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1 [Member] | Defined Benefit Plan, Debt Security Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1 [Member] | Defined Benefit Plan, Cash and Short-term Investments Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [1] | 0 |  |
Fair Value, Inputs, Level 1 [Member] | Other Investments [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 2 [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 2 [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 2 [Member] | Defined Benefit Plan, Equity Securities Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 2 [Member] | Defined Benefit Plan, Real Estate Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 2 [Member] | Defined Benefit Plan, Debt Security Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 2 [Member] | Defined Benefit Plan, Cash and Short-term Investments Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [1] | 0 |  |
Fair Value, Inputs, Level 2 [Member] | Other Investments [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Defined Benefit Plan, Equity Securities Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Defined Benefit Plan, Real Estate Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Defined Benefit Plan, Debt Security Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Defined Benefit Plan, Cash and Short-term Investments Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [1] | 0 |  |
Fair Value, Inputs, Level 3 [Member] | Other Investments [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] |  |  |  |
Plan Assets, Amount |  | 29,427 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Plan Assets, Amount |  | 29,427 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] | Defined Benefit Plan, Equity Securities Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] | Defined Benefit Plan, Real Estate Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] | Defined Benefit Plan, Debt Security Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] | Defined Benefit Plan, Cash and Short-term Investments Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [1] | 0 |  |
Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] | Other Investments [Member] |  |  |  |
Plan Assets, Amount |  | 0 |  |
Fair Value Measured at Net Asset Value Per Share [Member] |  |  |  |
Plan Assets, Amount | [2] | 298,439 |  |
Fair Value Measured at Net Asset Value Per Share [Member] | Defined Benefit Plan, Equity Securities [Member] |  |  |  |
Plan Assets, Amount | [2] | 0 |  |
Fair Value Measured at Net Asset Value Per Share [Member] | Defined Benefit Plan, Equity Securities Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [2] | 40,969 |  |
Fair Value Measured at Net Asset Value Per Share [Member] | Defined Benefit Plan, Real Estate Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [2] | 23,200 |  |
Fair Value Measured at Net Asset Value Per Share [Member] | Defined Benefit Plan, Debt Security Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [2] | 200,224 |  |
Fair Value Measured at Net Asset Value Per Share [Member] | Defined Benefit Plan, Cash and Short-term Investments Held in Common Collective Trusts [Member] |  |  |  |
Plan Assets, Amount | [1],[2] | 22,224 |  |
Fair Value Measured at Net Asset Value Per Share [Member] | Other Investments [Member] |  |  |  |
Plan Assets, Amount | [2] | $ 11,822 |  |
[1] | The cash/short term investments consist of a money market fund that holds individual, high quality, short duration fixed income investments, however the fund does not trade on public markets. The Company elected to consistently apply the practical expedient to all investments within common/collective trusts, and therefore, the fair value of this fund is measured at net asset value per share.
[2] | Certain investments that are measured at fair value using the net asset value per share (or its equivalent) practical expedient have not been categorized in the fair value hierarchy but are included to reconcile to the amounts presented in our Obligations and Funded Status table.

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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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