CONDENSED CONSOLIDATED STATEMENTS OF CAPITAL STOCK AND LONG-TERM DEBT - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Common Stock, No Par Value	$ 156,251	$ 155,120
Retained Earnings	79,826	74,055
TOTAL COMMON EQUITY	236,077	229,175
TOTAL PREFERRED STOCK	2,433	2,433
SUBTOTAL LONG-TERM DEBT	151,276	147,852
Add: Premium on Issuance of Long-term Debt	1,369	1,367
Less: Unamortized Debt Expense	(3,280)	(3,309)
Less: Current Portion of Long-term Debt	(7,236)	(6,865)
TOTAL LONG-TERM DEBT	142,129	139,045
Amortizing Secured Note, due December 20, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	1,055	1,180
Amortizing Secured Note, due May 19, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	4,165	4,375
Amortizing Secured Note, due August 25, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	3,407	3,547
Amortizing Secured Note, due September 19, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	3,687	3,827
State Revolving Trust Note, due December 31, 2022 [Member]
SUBTOTAL LONG-TERM DEBT	253	279
State Revolving Trust Note, due May 1, 2025 [Member]
SUBTOTAL LONG-TERM DEBT	1,743	1,851
State Revolving Trust Note, due March 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	372	392
State Revolving Trust Note, due January 25, 2027 [Member]
SUBTOTAL LONG-TERM DEBT	408	427
State Revolving Trust Note, due December 1, 2026 [Member]
SUBTOTAL LONG-TERM DEBT	527	553
State Revolving Trust Bond 4.00% to 5.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	162	162
State Revolving Trust Bond 0.00%, due August 1, 2021 [Member]
SUBTOTAL LONG-TERM DEBT	124	128
State Revolving Trust Note, due January 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	80	84
State Revolving Trust Note, due July 1, 2028 [Member]
SUBTOTAL LONG-TERM DEBT	246	256
State Revolving Trust Note, due August 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	935	962
Amortizing Secured Note, due April 20, 2029 [Member]
SUBTOTAL LONG-TERM DEBT	3,779	3,953
Amortizing Secured Note 7.05%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	2,896	3,021
Amortizing Secured Note 5.69%, due January 20, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	5,940	6,197
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	9,607	9,827
Amortizing Secured Note, due April 20, 2040 [Member]
SUBTOTAL LONG-TERM DEBT	3,566	3,646
State Revolving Trust Note, due July 1, 2031 [Member]
SUBTOTAL LONG-TERM DEBT	2,015	2,075
State Revolving Trust Note, due November 30, 2030 [Member]
SUBTOTAL LONG-TERM DEBT	1,057	1,090
Construction Loans [Member]
SUBTOTAL LONG-TERM DEBT		3,874
First Mortgage Bonds - Series X [Member]
SUBTOTAL LONG-TERM DEBT	54	55
First Mortgage Bonds - Series Y [Member]
SUBTOTAL LONG-TERM DEBT	61	61
First Mortgage Bonds - Series Z [Member]
SUBTOTAL LONG-TERM DEBT	221	224
First Mortgage Bonds - Series AA [Member]
SUBTOTAL LONG-TERM DEBT	300	300
First Mortgage Bonds - Series BB [Member]
SUBTOTAL LONG-TERM DEBT	471	482
First Mortgage Bonds - Series CC [Member]
SUBTOTAL LONG-TERM DEBT	636	636
First Mortgage Bonds - Series EE [Member]
SUBTOTAL LONG-TERM DEBT	2,231	2,296
First Mortgage Bonds - Series FF [Member]
SUBTOTAL LONG-TERM DEBT	3,495	3,495
First Mortgage Bonds - Series GG [Member]
SUBTOTAL LONG-TERM DEBT	799	813
First Mortgage Bonds - Series HH [Member]
SUBTOTAL LONG-TERM DEBT	880	880
First Mortgage Bonds - Series II [Member]
SUBTOTAL LONG-TERM DEBT	594	610
First Mortgage Bonds - Series JJ [Member]
SUBTOTAL LONG-TERM DEBT	750	750
First Mortgage Bonds - Series KK [Member]
SUBTOTAL LONG-TERM DEBT	969	988
First Mortgage Bonds - Series LL [Member]
SUBTOTAL LONG-TERM DEBT	1,095	1,095
First Mortgage Bonds - Series MM [Member]
SUBTOTAL LONG-TERM DEBT	1,203	1,237
First Mortgage Bonds - Series NN [Member]
SUBTOTAL LONG-TERM DEBT	1,505	1,505
First Mortgage Bonds - Series OO [Member]
SUBTOTAL LONG-TERM DEBT	2,057	2,107
First Mortgage Bonds - Series PP [Member]
SUBTOTAL LONG-TERM DEBT	740	740
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	2,208	2,258
First Mortgage Bonds - Series UU [Member]
SUBTOTAL LONG-TERM DEBT	845	845
First Mortgage Bonds - Series VV [Member]
SUBTOTAL LONG-TERM DEBT	2,243	2,290
First Mortgage Bonds - Series WW [Member]
SUBTOTAL LONG-TERM DEBT	830	830
First Mortgage Bonds - Series XX [Member]
SUBTOTAL LONG-TERM DEBT	11,259	11,259
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	7,076
3.00% to 5.00%, Series 2018B, due August 1, 2047 [Member]
SUBTOTAL LONG-TERM DEBT	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	$ 1,090	$ 1,115