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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 of hedged item in hedging relationship. Excludes hedged asset or liability.

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Fair value of all derivative assets designated as fair value hedging instruments.

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Amount of asset hedged in fair value hedging relationship.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. 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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Debt - Schedule of Long-Term Debt (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018	Feb. 28, 2018	Nov. 30, 2014
Debt Instrument [Line Items]
Fair value of interest rate swaps	$ 2,911,000
Fair value of interest rate swaps		$ (5,600,000)
Interest rate swap principal	200,000,000	200,000,000
Unamortized debt issuance costs	(7,272,000)	(7,820,000)
Revolving Credit Facility	0	0
Long-term Debt	$ 795,639,000	$ 786,580,000
Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.65%	4.65%		4.65%
Senior notes	$ 500,000,000	$ 500,000,000		$ 500,000,000
Interest rate swap principal	$ 200,000,000
Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	6.00%	6.00%	6.00%
Senior notes	$ 300,000,000	$ 300,000,000	$ 300,000,000