Commitments and Contingencies (details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Leases [Abstract]
Land Buildings And Equipment Expiration Date	through 2108
Operating Leases, Rent Expense, Minimum Rentals	$ 5,100,000.0	$ 4,800,000.0	$ 5,400,000.0
Operating And Capital Leases Table [Abstract]
Operating Leases, Future Minimum Payments Due, Current	5,611,000
Operating Leases, Future Minimum Payments, Due in Two Years	5,530,000
Operating Leases, Future Minimum Payments, Due in Three Years	5,510,000
Operating Leases, Future Minimum Payments, Due in Four Years	5,506,000
Operating Leases, Future Minimum Payments, Due in Five Years	2,858,000
Operating Leases, Future Minimum Payments, Due Thereafter	34,836,000
Operating Leases, Future Minimum Payments Due	59,851,000
Capital Leases, Future Minimum Payments Due, Current	462,000
Capital Leases, Future Minimum Payments Due in Two Years	196,000
Capital Leases, Future Minimum Payments Due in Three Years	82,000
Capital Leases, Future Minimum Payments Due in Four Years	12,000
Capital Leases, Future Minimum Payments Due in Five Years	0
Capital Leases, Future Minimum Payments Due Thereafter	0
Capital Leases, Future Minimum Payments Due	752,000
Future Minimum Payments Due Current	6,073,000
Future Minimum Payments Due In Two Years	5,726,000
Future Minimum Payments Due In Three Years	5,592,000
Future Minimum Payments Due In Four Years	5,518,000
Future Minimum Payments Due In Five Years	2,858,000
Future Minimum Payments Due Thereafter	34,836,000
Future Minimum Payments Due Total	60,603,000
Unrecorded Unconditional Purchase Obligations [Abstract]
Unrecorded Unconditional Purchase Obligation, Purchases	98,200,000	94,300,000	94,200,000
Unrecorded Unconditional Purchase Obligation Offsetting Sales	4,500,000	4,200,000	3,100,000
Gas Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	60,692,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	60,692,000
Unrecorded Unconditional Purchase Obligation Amount Representing Interest	20,000
Unrecorded Unconditional Purchase Obligation Total At Present Value	60,672,000
Pipeline Capacity Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	94,923,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	77,433,000
Unrecorded Unconditional Purchase Obligation, Due within Three Years	66,146,000
Unrecorded Unconditional Purchase Obligation, Due within Four Years	52,084,000
Unrecorded Unconditional Purchase Obligation, Due within Five Years	42,263,000
Unrecorded Unconditional Purchase Obligation, Due after Five Years	216,995,000
Unrecorded Unconditional Purchase Obligation	549,844,000
Unrecorded Unconditional Purchase Obligation Amount Representing Interest	113,437,000
Unrecorded Unconditional Purchase Obligation Total At Present Value	436,407,000
Pipeline Capacity Release Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	3,739,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	3,739,000
Unrecorded Unconditional Purchase Obligation Amount Representing Interest	0
Unrecorded Unconditional Purchase Obligation Total At Present Value	$ 3,739,000