Fair Value of Financial Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Dec. 31, 2012
Fair Value of Financial Assets and Liabilities
Risk premium (as a percent)	1.19%
Advances for construction	$ 184,879	$ 187,584
Level 1
Fair Value of Financial Assets and Liabilities
Money Market Investment	48,847
Total assets	48,847
Level 2
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities	570,058	613,211
Advances for construction	71,242	70,914
Total liabilities	641,300	684,125
Total
Fair Value of Financial Assets and Liabilities
Money Market Investment	48,847
Total assets	48,847
Long-term debt, including current maturities	570,058	613,211
Advances for construction	71,242	70,914
Total liabilities	641,300	684,125
Cost
Fair Value of Financial Assets and Liabilities
Money Market Investment	48,847
Total assets	48,847
Long-term debt, including current maturities	478,240	481,250
Advances for construction	184,879	187,584
Total liabilities	$ 663,119	$ 668,834

Represents the risk premium rate as an input to measure fair value.

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258

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- Definition

For utilities only, represents the carrying amount of the liability as of the balance sheet date for payments received by a utility from its customers in advance of performing its obligations under terms of its construction agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 910

-SubTopic 405

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6471548&loc=d3e50628-109371

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

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- Definition

Fair value of financial and nonfinancial obligations.

+ References

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- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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