Debt (Details 1) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	May 31, 2015
Debt Instrument, Face Amount			$ 50,000
Total	$ 384,073	$ 259,122
Senior Notes [Member]
Total Principal	385,000	260,000
Unamortized debt issuance costs	(927)	(878)
Total	384,073	259,122
Senior Notes [Member] \| 2025 Senior Unsecured Notes [Member]
Debt Instrument, Face Amount	50,000	50,000
Senior Notes [Member] \| 2027 Senior Unsecured Notes [Member]
Debt Instrument, Face Amount	50,000	50,000
Senior Notes [Member] \| 2028 Senior Unsecured Notes [Member]
Debt Instrument, Face Amount	60,000	60,000
Senior Notes [Member] \| 2029 Senior Unsecured Notes [Member]
Debt Instrument, Face Amount	100,000	100,000
Senior Notes [Member] \| 2030 Senior Unsecured Notes [Member]
Debt Instrument, Face Amount	$ 125,000	$ 0

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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- Definition

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

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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- Definition

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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