CONDENSED CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Common Stock, No Par Value	$ 165,138	$ 157,354
Retained Earnings	98,146	91,433
TOTAL COMMON EQUITY	263,284	248,787
TOTAL PREFERRED STOCK	2,433	2,433
SUBTOTAL LONG-TERM DEBT	173,634	162,904
Add: Premium on Issuance of Long-term Debt	1,150	1,259
Less: Unamortized Debt Expense	(3,857)	(3,969)
Less: Current Portion of Long-term Debt	(7,353)	(7,343)
TOTAL LONG-TERM DEBT	163,574	152,851
Amortizing Secured Note, due December 20, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	786	924
Amortizing Secured Note, due May 19, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	3,745	3,955
Amortizing Secured Note, due August 25, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	3,127	3,267
Amortizing Secured Note, due September 19, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	3,407	3,547
State Revolving Trust Note, due December 31, 2022 [Member]
SUBTOTAL LONG-TERM DEBT	202	228
State Revolving Trust Note, due May 1, 2025 [Member]
SUBTOTAL LONG-TERM DEBT	1,519	1,632
State Revolving Trust Note, due March 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	330	351
State Revolving Trust Note, due January 25, 2027 [Member]
SUBTOTAL LONG-TERM DEBT	369	389
State Revolving Trust Note, due December 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	474	501
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	111	111
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	85	88
State Revolving Trust Note, due July 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	225	235
State Revolving Trust Note, due January 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	73	77
State Revolving Trust Note, due August 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	880	907
Amortizing Secured Note, due April 20, 2029 [Member]
SUBTOTAL LONG-TERM DEBT	3,430	3,604
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	2,646	2,771
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	5,427	5,684
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	9,167	9,387
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	3,401	3,483
State Revolving Trust Note, due July 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	1,892	1,954
State Revolving Trust Note, due November 30, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	990	1,024
Construction Loans [Member]
SUBTOTAL LONG-TERM DEBT	29,726	16,509
First Mortgage Bonds - Series Z [Member]
SUBTOTAL LONG-TERM DEBT	113	113
First Mortgage Bonds - Series AA [Member]
SUBTOTAL LONG-TERM DEBT	155	155
First Mortgage Bonds - Series BB [Member]
SUBTOTAL LONG-TERM DEBT	354	362
First Mortgage Bonds - Series CC [Member]
SUBTOTAL LONG-TERM DEBT	489	489
First Mortgage Bonds - Series EE [Member]
SUBTOTAL LONG-TERM DEBT	1,818	1,876
First Mortgage Bonds - Series FF [Member]
SUBTOTAL LONG-TERM DEBT	2,980	2,980
First Mortgage Bonds - Series GG [Member]
SUBTOTAL LONG-TERM DEBT	710	723
First Mortgage Bonds - Series HH [Member]
SUBTOTAL LONG-TERM DEBT	795	795
First Mortgage Bonds - Series II [Member]
SUBTOTAL LONG-TERM DEBT	506	520
First Mortgage Bonds - Series JJ [Member]
SUBTOTAL LONG-TERM DEBT	671	671
First Mortgage Bonds - Series KK [Member]
SUBTOTAL LONG-TERM DEBT	880	898
First Mortgage Bonds - Series LL [Member]
SUBTOTAL LONG-TERM DEBT	1,010	1,010
First Mortgage Bonds - Series MM [Member]
SUBTOTAL LONG-TERM DEBT	1,103	1,137
First Mortgage Bonds - Series NN [Member]
SUBTOTAL LONG-TERM DEBT	1,285	1,415
First Mortgage Bonds - Series OO [Member]
SUBTOTAL LONG-TERM DEBT	1,906	1,956
First Mortgage Bonds - Series PP [Member]
SUBTOTAL LONG-TERM DEBT	700	700
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	2,057	2,107
First Mortgage Bonds - Series UU [Member]
SUBTOTAL LONG-TERM DEBT	800	800
First Mortgage Bonds - Series VV [Member]
SUBTOTAL LONG-TERM DEBT	2,099	2,147
First Mortgage Bonds - Series WW [Member]
SUBTOTAL LONG-TERM DEBT	795	795
First Mortgage Bonds - Series XX [Member]
SUBTOTAL LONG-TERM DEBT	10,880	11,006
First Mortgage Bonds - Series YY [Member]
SUBTOTAL LONG-TERM DEBT	3,860	3,860
0.00%, Series 2018A, due August 1, 2047 [Member]
SUBTOTAL LONG-TERM DEBT	6,837	6,917
3.00%-5.00%, Series 2018B, due August 1, 2047 [Member]
SUBTOTAL LONG-TERM DEBT	2,365	2,365
Convertible Preferred Stock $7.00 Series [Member]
TOTAL PREFERRED STOCK	1,005	1,005
Convertible Preferred Stock $8.00 Series [Member]
TOTAL PREFERRED STOCK	349	349
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
State Revolving Trust Note, due February 1, 2036 [Member]
SUBTOTAL LONG-TERM DEBT	$ 1,039	$ 1,064