CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT (Parenthetical) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Common Stock, Shares Authorized	40,000	40,000
Common Stock, Shares Outstanding	17,473	17,434
Preferred Stock, Shares Authorized	120	120
Preferred Stock, Shares Outstanding	20	20
Convertible Preferred Stock $7.00 Series
Common Stock, Shares Outstanding	10	10
Nonredeemable Preferred Stock $7.00 Series
Common Stock, Shares Outstanding	1	1
Nonredeemable Preferred Stock $4.75 Series [Member]
Common Stock, Shares Outstanding	10	10
Amortizing Secured Note, due December 20, 2021 [Member]
Due date of debt	Dec. 20, 2021
Interest rate	8.05%
Amortizing Secured Note, due May 19, 2028 [Member]
Due date of debt	May 19, 2028
Interest rate	6.25%
Amortizing Secured Note, due August 25, 2030 [Member]
Due date of debt	Aug. 25, 2030
Interest rate	6.44%
Amortizing Secured Note, due September 19, 2031 [Member]
Due date of debt	Sep. 19, 2031
Interest rate	6.46%
State Revolving Trust Note, due December 31, 2022 [Member]
Due date of debt	Dec. 31, 2022
Interest rate	4.22%
State Revolving Trust Note, due May 1, 2025 [Member]
Due date of debt	May 01, 2025
Interest rate	3.60%
State Revolving Trust Note, due March 1, 2026 [Member]
Due date of debt	Mar. 01, 2026
Interest rate	3.30%
State Revolving Trust Note, due January 25, 2027 [Member]
Due date of debt	Jan. 25, 2027
Interest rate	3.49%
State Revolving Trust Note, due December 1, 2026 [Member]
Due date of debt	Dec. 01, 2026
Interest rate	4.03%
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
Due date of debt	Aug. 01, 2021
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
Due date of debt	Aug. 01, 2021
Interest rate	0.00%
State Revolving Trust Note, due July 1, 2028 [Member]
Due date of debt	Jul. 01, 2028
Interest rate	3.64%
State Revolving Trust Note, due January 1, 2028 [Member]
Due date of debt	Jan. 01, 2028
Interest rate	3.64%
State Revolving Trust Note, due August 1, 2031 [Member]
Due date of debt	Aug. 01, 2031
Interest rate	3.45%
Amortizing Secured Note, due April 20, 2029 [Member]
Due date of debt	Apr. 20, 2029
Interest rate	6.59%
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
Due date of debt	Jan. 20, 2030
Interest rate	7.05%
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
Due date of debt	Jan. 20, 2030
Interest rate	5.69%
4.45%, Amortizing Secured Note, due April 20, 2040 [Member]
Due date of debt	Apr. 20, 2040
Interest rate	4.45%
4.47%, Amortizing Secured Note, due April 20, 2040 [Member]
Due date of debt	Apr. 20, 2040
Interest rate	4.47%
State Revolving Trust Note, due July 1, 2031 [Member]
Due date of debt	Jul. 01, 2031
Interest rate	3.75%
State Revolving Trust Note, due February 1, 2036 [Member]
Due date of debt	Feb. 01, 2036
Interest rate	2.00%
State Revolving Trust Note, due February 1, 2038 [Member]
Due date of debt	Nov. 01, 2038
Interest rate	2.00%
State Revolving Trust Note, due November 30, 2030 [Member]
Due date of debt	Nov. 30, 2030
Interest rate	3.75%
Construction Loans [Member]
Interest rate	0.00%
First Mortgage Bonds - Series BB [Member]
Due date of debt	Aug. 01, 2021
Interest rate	0.00%
First Mortgage Bonds - Series CC [Member]
Due date of debt	Aug. 01, 2021
First Mortgage Bonds - Series CC [Member] | Minimum [Member]
Interest rate	4.00%
First Mortgage Bonds - Series CC [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series EE [Member]
Due date of debt	Aug. 01, 2023
Interest rate	0.00%
First Mortgage Bonds - Series FF [Member]
Due date of debt	Aug. 01, 2024
First Mortgage Bonds - Series FF [Member] | Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series FF [Member] | Maximum [Member]
Interest rate	5.50%
First Mortgage Bonds - Series GG [Member]
Due date of debt	Aug. 01, 2026
Interest rate	0.00%
First Mortgage Bonds - Series HH [Member]
Due date of debt	Aug. 01, 2026
First Mortgage Bonds - Series HH [Member] | Minimum [Member]
Interest rate	4.00%
First Mortgage Bonds - Series HH [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series II [Member]
Due date of debt	Aug. 01, 2024
Interest rate	0.00%
First Mortgage Bonds - Series JJ [Member]
Due date of debt	Aug. 01, 2027
First Mortgage Bonds - Series JJ [Member] | Minimum [Member]
Interest rate	3.40%
First Mortgage Bonds - Series JJ [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series KK [Member]
Due date of debt	Aug. 01, 2028
Interest rate	0.00%
First Mortgage Bonds - Series LL [Member]
Due date of debt	Aug. 01, 2028
First Mortgage Bonds - Series LL [Member] | Minimum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series LL [Member] | Maximum [Member]
Interest rate	5.50%
First Mortgage Bonds - Series MM [Member]
Due date of debt	Aug. 01, 2030
Interest rate	0.00%
First Mortgage Bonds - Series NN [Member]
Due date of debt	Aug. 01, 2030
First Mortgage Bonds - Series NN [Member] | Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series NN [Member] | Maximum [Member]
Interest rate	4.375%
First Mortgage Bonds - Series OO [Member]
Due date of debt	Aug. 01, 2031
Interest rate	0.00%
First Mortgage Bonds - Series PP [Member]
Due date of debt	Aug. 01, 2031
First Mortgage Bonds - Series PP [Member] | Minimum [Member]
Interest rate	2.00%
First Mortgage Bonds - Series PP [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series QQ [Member]
Due date of debt	Oct. 01, 2023
Interest rate	5.00%
First Mortgage Bonds - Series RR [Member]
Due date of debt	Oct. 01, 2038
Interest rate	3.80%
First Mortgage Bonds - Series SS [Member]
Due date of debt	Oct. 01, 2047
Interest rate	4.25%
First Mortgage Bonds - Series TT [Member]
Due date of debt	Aug. 01, 2032
Interest rate	0.00%
First Mortgage Bonds - Series UU [Member]
Due date of debt	Aug. 01, 2032
First Mortgage Bonds - Series UU [Member] | Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series UU [Member] | Maximum [Member]
Interest rate	3.25%
First Mortgage Bonds - Series VV [Member]
Due date of debt	Aug. 01, 2033
Interest rate	0.00%
First Mortgage Bonds - Series WW [Member]
Due date of debt	Aug. 01, 2033
First Mortgage Bonds - Series WW [Member] | Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series WW [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series XX [Member]
Due date of debt	Aug. 01, 2047
Interest rate	0.00%
First Mortgage Bonds - Series YY [Member]
Due date of debt	Aug. 01, 2047
First Mortgage Bonds - Series YY [Member] | Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series YY [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series 2018A [Member]
Due date of debt	Aug. 01, 2047
Interest rate	0.00%
First Mortgage Bonds - Series 2018B [Member]
Due date of debt	Aug. 01, 2047
First Mortgage Bonds - Series 2018B [Member] | Minimum [Member]
Interest rate	3.00%
First Mortgage Bonds - Series 2018B [Member] | Maximum [Member]
Interest rate	5.00%
First Mortgage Bonds - Series 2019A [Member]
Due date of debt	Aug. 01, 2059
Interest rate	4.00%
First Mortgage Bonds - Series 2019B [Member]
Due date of debt	Aug. 01, 2059
Interest rate	5.00%
First Mortgage Bonds - Series 2020A [Member]
Due date of debt	Nov. 18, 2050
Interest rate	2.90%