Balance Sheet Components - Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Accrued taxes other than income taxes	$ 38,734	$ 36,965
Employee paid time off accruals	25,728	22,343
Accrued interest	16,226	16,486
Current portion of pensions and other postretirement benefits	11,700	8,826
Income taxes payable	0	298
Derivative liabilities	3,064	10,928
Other current liabilities	27,806	35,133
Total other current liabilities	$ 123,258	$ 130,979

Carrying value as of the balance sheet date of obligations incurred and payable for real and property taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred and payable for unused vacation time owed to employees based on the entity's vacation benefit given to its employees. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Current liabilities attributable to energy marketing activities (trading activities). Current energy marketing (trading activities) are when entities engage in both financial and physical trading to increase profits, manage their commodity price risk and enhance system reliability. They may trade electricity, coal, natural gas and oil. These entities typically use a variety of financial instruments, including forward contracts, options and swaps.

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer.

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Amount of liability, recognized in statement of financial position, for defined benefit pension and other postretirement plans, classified as current.

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Carrying value as of the balance sheet date of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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