Long-Term Debt and Short-Term Borrowings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 84,975	$ 85,017
Less current maturities	(42)	(42)
Long-term portion	84,933	84,975
Payments due by year [Abstract]
2013	42
2014	12,043
2015	43
2016	7,344
2017	44
Long Term debt [Abstract]
Maximum borrowing percentage of utility plant (in hundredths)	60.00%
Base amount added to annual net income to determine restriction on dividends and stock acquisition	1,500
Line of Credit Facility [Abstract]
Unsecured lines of credit aggregating amount	29,000
Number of banks in wich unsecured line of credit maintained	3
Line of credit compensating balance requirement	500	500
Unsecured Line of Credit, First Note [Member]
Line of Credit Facility [Abstract]
Unsecured lines of credit aggregating amount	13,000
Line of credit maturity date	May 01, 2014
Basis for interest rate	LIBOR plus 1.20%
Line of credit amount outstanding	0	0
Unsecured Line of Credit, Second Note [Member]
Line of Credit Facility [Abstract]
Unsecured lines of credit aggregating amount	11,000
Line of credit maturity date	May 01, 2014
Basis for interest rate	LIBOR plus 1.25%
Line of credit compensating balance requirement	500
Line of credit amount outstanding	0	0
Unsecured Line of Credit, Third Note [Member]
Line of Credit Facility [Abstract]
Unsecured lines of credit aggregating amount	5,000
Line of credit maturity date	Jun. 01, 2013
Basis for interest rate	LIBOR plus 1.50%
Line of credit amount outstanding	0	0
Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Bonds, Series A, due 2016, 4.05 Percent [Member]
Debt Instrument [Line Items]
Long-term debt	2,350	2,350
Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Bonds, Series A, due 2016, 5.00 Percent [Member
Debt Instrument [Line Items]
Long-term debt	4,950	4,950
Senior Notes, Series A, due 2019, 10.17 percent [Member]
Debt Instrument [Line Items]
Long-term debt	6,000	6,000
Senior Notes, Series B, due 2019, 9.6 percent [Member]
Debt Instrument [Line Items]
Long-term debt	5,000	5,000
Pennvest Loan, due 2019, 1.00 percent [Member]
Debt Instrument [Line Items]
Long-term debt	290	332
Long Term debt [Abstract]
Amount of receivables as collateral	800
Senior Notes, Series C, due 2020, 10.05 percent [Member]
Debt Instrument [Line Items]
Long-term debt	6,500	6,500
Senior Notes, Series D, due 2022, 8.43 percent [Member]
Debt Instrument [Line Items]
Long-term debt	7,500	7,500
Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Bonds Series 2008A due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt	12,000	12,000
Long Term debt [Abstract]
Variable interest rate, annual average (in hundredths)	0.19%	0.20%
Variable interest rate, at year end (in hundredths)	0.14%	0.09%
Interest Rate Swap Derivatives [Abstract]
Notional amount of swap	12,000
Fixed interest rate paid to the counterparty (in hundredths)	3.16%
Net payment rate on swap (in hundredths)	3.01%	3.01%
Potential payment to counterparty	3,028
Interest rate spread in basis points	2	8
Overall effective rate, including variable interest and swap payments (in hundredths)	3.18%	3.08%
Basis for floating interest rate paid to the Company	59% of the U.S. Dollar one-month LIBOR rate
Variable Rate Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Bonds Series 2008A due 2029 [Member] | Letter of Credit [Member]
Line of Credit Facility [Abstract]
Line of credit maturity date	May 06, 2015
Industrial Development Authority Revenue Bonds, series 2006, due 2036, 4.75 percent [Member]
Debt Instrument [Line Items]
Long-term debt	10,500	10,500
Pennsylvania Economic Development Financing Authority Exempt Facilities Revenue Bonds, Series 2008B, due 2038, 6.00 percent [Member]
Debt Instrument [Line Items]
Long-term debt	14,885	14,885
Long Term debt [Abstract]
Special provision, amount to be redeemed per individual interest, per year, maximum	25
Special provision, amount to be redeemed in the aggregate, per year, maximum	300
Special provision, repayment of bonds	0	115
Monthly Senior Notes, Series 2010A, due 2040, 5.00 percent [Member]
Debt Instrument [Line Items]
Long-term debt	$ 15,000	$ 15,000