CONDENSED CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Common Stock, No Par Value	$ 216,866	$ 215,125
Retained Earnings	125,240	108,667
TOTAL COMMON EQUITY	342,106	323,792
TOTAL PREFERRED STOCK	2,084	2,084
SUBTOTAL LONG-TERM DEBT	238,326	234,397
Add: Premium on Issuance of Long-term Debt	7,766	8,064
Less: Unamortized Debt Expense	(4,364)	(4,506)
Less: Current Portion of Long-term Debt	(7,239)	(7,178)
TOTAL LONG-TERM DEBT	234,489	230,777
Amortizing Secured Note, due December 20, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	415	643
Amortizing Secured Note, due May 19, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	3,220	3,535
Amortizing Secured Note, due August 25, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	2,777	2,987
Amortizing Secured Note, due September 19, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	3,057	3,267
State Revolving Trust Note, due December 31, 2022 [Member]
SUBTOTAL LONG-TERM DEBT	147	175
State Revolving Trust Note, due May 1, 2025 [Member]
SUBTOTAL LONG-TERM DEBT	1,288	1,405
State Revolving Trust Note, due March 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	266	309
State Revolving Trust Note, due January 25, 2027 [Member]
SUBTOTAL LONG-TERM DEBT	307	349
State Revolving Trust Note, due December 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	419	446
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	4	60
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	11	50
State Revolving Trust Note, due July 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	203	214
State Revolving Trust Note, due January 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	66	69
State Revolving Trust Note, due August 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	793	851
Amortizing Secured Note, due April 20, 2029 [Member]
SUBTOTAL LONG-TERM DEBT	2,994	3,255
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	2,333	2,521
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	4,786	5,171
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	8,617	8,946
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	3,197	3,320
State Revolving Trust Note, due July 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	1,765	1,829
State Revolving Trust Note, due February 1, 2036 [Member]
SUBTOTAL LONG-TERM DEBT	960	1,013
State Revolving Trust Note, due November 1, 2038 [Member]
SUBTOTAL LONG-TERM DEBT	1,579	1,309
State Revolving Trust Note, due November 30, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	919	955
Construction Loans [Member]
SUBTOTAL LONG-TERM DEBT	50,536	40,467
First Mortgage Bonds - Series BB [Member]
SUBTOTAL LONG-TERM DEBT	119	241
First Mortgage Bonds - Series CC [Member]
SUBTOTAL LONG-TERM DEBT	164	331
First Mortgage Bonds - Series EE [Member]
SUBTOTAL LONG-TERM DEBT	1,036	1,456
First Mortgage Bonds - Series FF [Member]
SUBTOTAL LONG-TERM DEBT	1,870	2,440
First Mortgage Bonds - Series GG [Member]
SUBTOTAL LONG-TERM DEBT	542	632
First Mortgage Bonds - Series HH [Member]
SUBTOTAL LONG-TERM DEBT	620	710
First Mortgage Bonds - Series II [Member]
SUBTOTAL LONG-TERM DEBT	338	429
First Mortgage Bonds - Series JJ [Member]
SUBTOTAL LONG-TERM DEBT	500	588
First Mortgage Bonds - Series KK [Member]
SUBTOTAL LONG-TERM DEBT	719	807
First Mortgage Bonds - Series LL [Member]
SUBTOTAL LONG-TERM DEBT	846	928
First Mortgage Bonds - Series MM [Member]
SUBTOTAL LONG-TERM DEBT	937	1,037
First Mortgage Bonds - Series NN [Member]
SUBTOTAL LONG-TERM DEBT	1,105	1,190
First Mortgage Bonds - Series OO [Member]
SUBTOTAL LONG-TERM DEBT	1,655	1,806
First Mortgage Bonds - Series PP [Member]
SUBTOTAL LONG-TERM DEBT	600	660
First Mortgage Bonds - Series QQ [Member]
SUBTOTAL LONG-TERM DEBT	9,915	9,915
First Mortgage Bonds - Series RR [Member]
SUBTOTAL LONG-TERM DEBT	22,500	22,500
First Mortgage Bonds - Series SS [Member]
SUBTOTAL LONG-TERM DEBT	23,000	23,000
First Mortgage Bonds - Series TT [Member]
SUBTOTAL LONG-TERM DEBT	1,806	1,957
First Mortgage Bonds - Series UU [Member]
SUBTOTAL LONG-TERM DEBT	705	755
First Mortgage Bonds - Series VV [Member]
SUBTOTAL LONG-TERM DEBT	1,861	2,004
First Mortgage Bonds - Series WW [Member]
SUBTOTAL LONG-TERM DEBT	715	755
First Mortgage Bonds - Series XX [Member]
SUBTOTAL LONG-TERM DEBT	10,247	10,627
First Mortgage Bonds - Series YY [Member]
SUBTOTAL LONG-TERM DEBT	3,710	3,785
0.00%, Series 2018A, due August 1, 2047 [Member]
SUBTOTAL LONG-TERM DEBT	6,247	6,678
3.00%-5.00%, Series 2018B, due August 1, 2047 [Member]
SUBTOTAL LONG-TERM DEBT	2,210	2,320
4.00%, Series 2019A, due August 1, 2059 [Member]
SUBTOTAL LONG-TERM DEBT	32,500	32,500
5.00%, Series 2019B, due August 1, 2059 [Member]
SUBTOTAL LONG-TERM DEBT	21,200	21,200
Convertible Preferred Stock $7.00 Series [Member]
TOTAL PREFERRED STOCK	1,005	1,005
Nonredeemable Preferred Stock $7.00 Series [Member]
TOTAL PREFERRED STOCK	79	79
Nonredeemable Preferred Stock $4.75 Series [Member]
TOTAL PREFERRED STOCK	$ 1,000	$ 1,000