Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	$ 6,797	$ 1,276
Commodity futures - financial liabilities	7,442	1,732
Long-term Debt.	3,102,676	2,734,344
Level 2
Assets and liabilities subject to fair value measurements
Fair value of long-term debt, including current maturities	3,400,000	2,800,000
Recurring
Assets and liabilities subject to fair value measurements
Short-term Investments		262,174
Recurring \| Level 2
Assets and liabilities subject to fair value measurements
Short-term Investments		262,174
Futures \| Recurring \| Commodity contract
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	6,797	1,276
Commodity futures - financial liabilities	7,442	1,732
Futures \| Recurring \| Level 2 \| Commodity contract
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	6,797	1,276
Commodity futures - financial liabilities	$ 7,442	$ 1,732

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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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 investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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