Face (par) amount of debt instrument at time of issuance.

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after accumulated amortization, of debt discount.

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Gross amount of debt extinguished.

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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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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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The sum of the fair values, as of the date of each statement of financial position presented, of securities that are restricted as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

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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, Financing Arrangements, and Leases Debt Disclosure (Details) - USD ($)	Jun. 15, 2018	Dec. 31, 2019	Dec. 31, 2018	Aug. 24, 2018
Debt Instrument [Line Items]
Long-term Debt		$ 577,045,000	$ 576,168,000
Debt issuance costs		(4,083,000)	(4,507,000)
Unamortized debt discount		(3,872,000)	(4,325,000)
Property pledged as collateral		0
Long-term Debt, Fiscal Year Maturity [Abstract]
2020		0
2021		0
2022		0
2023		0
2024		0
4% Senior Unsecured Notes Due 2027 [Member]
Debt Instrument [Line Items]
Issuance of debt				$ 250,000,000
7.125 percent unsecured debentures due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt		85,000,000	85,000,000
4.0% unsecured debentures due 2027 [Member]
Debt Instrument [Line Items]
Long-term Debt		$ 500,000,000	$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.00%
6.05 Percent Senior Unsecured Notes Due 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.05%
Extinguishment of Debt, Amount	$ 250,000,000