Debt Debt (Schedule of Long Term Debt Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Unsecured Debt	$ 400,000
Long-term Debt, Maturities, Repayments of Principal in Next Rolling Twelve Months	1,187
Long-term Debt, Maturities, Repayments of Principal in Rolling Year Two	1,230
Long-term Debt, Maturities, Repayments of Principal in Rolling Year Three	121,279
Long-term Debt, Maturities, Repayments of Principal in Rolling Year Four	335,328
Long-term Debt, Maturities, Repayments of Principal in Rolling Year Five	476,379
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	358,867
Long-term Debt, Gross	1,294,270
Debt Instrument, Unamortized Discount	(2,711)
Less: unamortized loan costs	9,884	$ 10,453
Debt, Long-term and Short-term, Combined Amount	1,281,675	1,145,497
Private Placement [Member]
Unsecured Debt	400,000	$ 400,000
January 2023 [Member]
Unsecured Debt	$ 125,000
Debt Instrument, Interest Rate, Stated Percentage	3.99%
November 2023 [Member]
Unsecured Debt	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	3.99%
September 2024 [Member]
Unsecured Debt	$ 75,000
Debt Instrument, Interest Rate, Stated Percentage	3.93%
November 2025 [Member]
Unsecured Debt	$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	4.33%
January 2027 [Member]
Unsecured Debt	$ 100,000
Debt Instrument, Interest Rate, Stated Percentage	4.51%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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

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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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