Fair Value of Financial Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Fair Value of Financial Assets and Liabilities
Risk premium (as a percent)	1.19%cwt_FairValueInputsRiskPremium
Advances for construction	$ 181,553us-gaap_CustomerAdvancesForConstruction	$ 182,284us-gaap_CustomerAdvancesForConstruction
Level 2
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities	544,493	534,068
Advances for construction	74,217	72,571
Total liabilities	618,710	606,639
Cost
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities	425,610	425,840
Advances for construction	181,553	182,284
Total liabilities	607,163	608,124
Total
Fair Value of Financial Assets and Liabilities
Long-term debt, including current maturities	544,493	534,068
Advances for construction	74,217	72,571
Total liabilities	$ 618,710	$ 606,639

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

No definition available.

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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

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

Fair value of financial and nonfinancial obligations.

+ 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=36462937&loc=d3e19207-110258

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