Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Provisions for income taxes [Abstract]
Federal current	$ 2,100	$ 1,357	$ 1,872
State current	1,195	413	1,115
Federal deferred	2,371	3,291	2,645
State deferred	(21)	(63)	(16)
Federal investment tax credit, net of current utilization	(39)	(39)	(38)
Total income taxes	5,606	4,959	5,578
Reconciliation of statutory Federal tax provision [Abstract]
Statutory Federal tax provision	5,069	4,775	4,933
State income taxes, net of Federal benefit	775	231	725
Tax-exempt interest	(33)	(32)	(37)
Amortization of investment tax credit	(39)	(39)	(38)
Cash value of life insurance	(27)	90	70
Domestic production deduction	(140)	(115)	(127)
Other, net	1	49	52
Total income taxes	5,606	4,959	5,578
Reconciliation of statutory Federal tax provision (in hundredths)	34.00%
Deferred tax assets [Abstract]
Reserve for doubtful accounts	124	135
Compensated absences	200	190
Deferred compensation	1,328	1,234
Customers' advances and contributions	37	57
Deferred taxes associated with the gross-up of revenues necessary to return, in rates, the effect of temporary differences	114	119
Pensions	4,895	4,776
Contributions carryover	0	36
Other costs deducted for book, not for tax	43	39
Total deferred tax assets	6,741	6,586
Deferred tax liabilities [Abstract]
Accelerated depreciation	30,454	27,850
Investment tax credit	482	505
Deferred taxes associated with the gross-up of revenues necessary to recover, in rates, the effect of temporary differences	1,991	1,864
Tax effect of pension regulatory asset	5,782	5,663
Other costs deducted for tax, not for book	249	285
Total deferred tax liabilities	38,958	36,167
Net deferred tax liability	32,217	29,581
Reflected on balance sheets as [Abstract]
Current deferred tax asset	(208)	(228)
Noncurrent deferred tax liability	32,425	29,809
Net deferred tax liability	32,217	29,581
Other Income Tax Disclosure [Abstract]
Valuation allowance	0	0
Open tax year		2011	2010	2009
Interest or penalties	$ 0	$ 0	$ 0