Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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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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Fair value amount of debt instrument that was repurchased.

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Amount, after accumulated amortization, of debt premium.

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Weighted average interest rate of debt outstanding.

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Amount of cash paid for interest capitalized, classified as investing activity.

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Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

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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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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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Long-Term Debt (Details) - USD ($)	12 Months Ended
Long-Term Debt (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 18, 2019	Jul. 17, 2019	Dec. 31, 2015	Apr. 30, 2014	Feb. 28, 2013
Debt Instrument [Line Items]
Total long-term debt	$ 569,788,000	$ 656,459,000
Cash paid for interest	48,025,000	50,543,000	$ 45,728,000
Capitalized interest	5,000	624,000	$ 730,000
Revolving Loan Facility
Debt Instrument [Line Items]
Total long-term debt	196,414,000	283,463,000
Face amount	400,000,000			$ 400,000,000	$ 500,000,000
Unamortized debt issuance costs	$ 4,586,000	3,537,000
Weighted average interest rate	5.26%
Revolving Loan Facility \| LIBOR
Debt Instrument [Line Items]
Applicable margins	3.50%
Revolving Loan Facility \| Minimum \| LIBOR
Debt Instrument [Line Items]
Applicable margins	2.25%
Revolving Loan Facility \| Minimum \| Prime Rate
Debt Instrument [Line Items]
Applicable margins	1.25%
Revolving Loan Facility \| Maximum \| LIBOR
Debt Instrument [Line Items]
Applicable margins	3.50%
Revolving Loan Facility \| Maximum \| Prime Rate
Debt Instrument [Line Items]
Applicable margins	2.50%
Senior Notes \| Senior Notes 7.250%
Debt Instrument [Line Items]
Total long-term debt	$ 373,374,000	372,996,000
Face amount	$ 400,000,000						$ 150,000,000	$ 250,000,000
Fixed rate cost	7.25%
Unamortized debt issuance costs	$ 770,000	1,454,000
Unamortized premium	$ 344,000	$ 650,000
Amount of debt repurchased						$ 26,200,000