Financing Activities (Details) - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Short-term Debt [Line Items]
Short term borrowings	$ 100,000	$ 0
Secured Debt Montana Due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 100,000
Debt Instrument, Interest Rate, Stated Percentage	3.21%
Long-term Debt, Maturity Date	May 15, 2030
Secured Debt South Dakota Due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	3.21%
Long-term Debt, Maturity Date	May 15, 2030
Term Loan Due 2021 [Member]
Short-term Debt [Line Items]
Short term borrowings	$ 100,000
Maximum Ratio Of Indebtedness To Net Capital Threshold Percentage	65.00%
Term Loan Due 2021 [Member] \| Eurodollar [Member]
Short-term Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.50%

Maximum Ratio Of Indebtedness To Net Capital Threshold Percentage

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
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-Paragraph 2
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Maturity date of long-term debt, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

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+ References

No definition available.

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