Contractual interest rate for funds borrowed, under the debt agreement.

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-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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Weighted average interest rate of long-term debt outstanding calculated at point in time.

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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Debt (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Long-term Debt		$ 809,594	$ 779,887	$ 779,424
Unamortized debt issuance costs		$ 5,940	$ 6,813	$ 7,276
Maturity start date range		Mar. 16, 2018
Maturity end date range		Sep. 10, 2048
Weighted average interest rate		4.69%
Minimum
Debt Instrument [Line Items]
Stated interest rate		1.545%
Maximum
Debt Instrument [Line Items]
Stated interest rate		9.05%
$22 Million Series 6.60% Due 2018
Debt Instrument [Line Items]
Stated interest rate	6.60%
Repayments of Debt	$ 22,000
$50 Million Series 4.11% Due 2048 [Member]
Debt Instrument [Line Items]
Stated interest rate		4.11%
Proceeds from Issuance of Debt		$ 50,000