DEBT, Long-Term Debt (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 144,090	$ 145,862
Less: current maturities (principal amount)	1,757	1,706
Total long-term debt	142,333	144,156
Payments of principal amounts due during the next five years and thereafter [Abstract]
2020	1,757
2021	1,544
2022	1,585
2023	1,520
2024	1,484
Thereafter	136,200
Promissory Note [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 11,279	11,648
Interest rate, stated percentage	5.12%
Maturity date	Dec. 30, 2028
First Mortgage Bonds [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 127,800	128,400
Payments of principal amounts due during the next five years and thereafter [Abstract]
2020	600
2021	600
2022	600
2023	600
2024	600
Thereafter	124,800
First Mortgage Bonds [Member] \| Series R [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 25,000	25,000
Interest rate, stated percentage	5.96%
Maturity date	Dec. 31, 2028
First Mortgage Bonds [Member] \| Series S [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 7,800	8,400
Interest rate, stated percentage	4.45%
Maturity date	Dec. 31, 2033
First Mortgage Bonds [Member] \| Series T [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 40,000	40,000
Interest rate, stated percentage	4.24%
Maturity date	Dec. 20, 2036
First Mortgage Bonds [Member] \| Series U [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 25,000	25,000
Interest rate, stated percentage	4.71%
Maturity date	Jan. 31, 2038
First Mortgage Bonds [Member] \| Series V [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 30,000	30,000
Interest rate, stated percentage	4.42%
Maturity date	Oct. 31, 2049
State Revolving Fund Loans [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 5,011	5,814
Payments of principal amounts due during the next five years and thereafter [Abstract]
2020	767
2021	533
2022	552
2023	466
2024	404
Thereafter	2,289
State Revolving Fund Loans [Member] \| 4.48%, due 08/01/2021 [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 318	622
Interest rate, stated percentage	4.48%
Maturity date	Aug. 01, 2021
State Revolving Fund Loans [Member] \| 3.57%, due 09/01/2023 [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 294	385
Interest rate, stated percentage	3.57%
Maturity date	Sep. 01, 2023
State Revolving Fund Loans [Member] \| 3.64%, due 05/01/2025 [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 648	778
Interest rate, stated percentage	3.64%
Maturity date	May 01, 2025
State Revolving Fund Loans [Member] \| 3.41%, due 02/01/2031 [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 1,887	2,034
Interest rate, stated percentage	3.41%
Maturity date	Feb. 01, 2031
State Revolving Fund Loans [Member] \| 3.40%, due 07/01/2032 [Member]
Long-term debt consists of [Abstract]
Promissory Note, 5.12%, due December 30, 2028	$ 1,864	$ 1,995
Interest rate, stated percentage	3.40%
Maturity date	Jul. 01, 2032
State Revolving Fund Loans [Member] \| Promissory Note [Member]
Payments of principal amounts due during the next five years and thereafter [Abstract]
2020	$ 390
2021	411
2022	433
2023	454
2024	480
Thereafter	$ 9,111

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 50
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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