Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Assets:
Investments	$ 9,895	$ 12,095
Energy Marketing Contracts Assets, Current	4,552	7,076
Liabilities:
Energy Marketing Contract Liabilities, Current	2,051	743
Equity Securities [Member]
Assets:
Investments	21	26
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Assets, Fair Value Disclosure	8,049	10,059
Quoted Prices in Active Markets (Level 1) [Member] \| Equity Securities [Member]
Assets:
Investments	21	26
Quoted Prices in Active Markets (Level 1) [Member] \| Investments - Mutual funds and other [Member]
Assets:
Investments	8,028	10,033
Quoted Prices in Active Markets (Level 1) [Member] \| Total Investments [Member]
Assets:
Investments	8,049	10,059
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, Fair Value Disclosure	4,552	7,076
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, Fair Value Disclosure	1,846	2,036
Significant Unobservable Inputs (Level 3) [Member] \| Investments in guaranteed income fund [Member]
Assets:
Investments	1,846	2,036
Significant Unobservable Inputs (Level 3) [Member] \| Total Investments [Member]
Assets:
Investments	1,846	2,036
Recurring [Member]
Assets:
Assets, Fair Value Disclosure	14,447	19,171
Liabilities:
Energy Marketing Contract Liabilities, Current		743
Recurring [Member] \| Equity Securities [Member]
Assets:
Investments	21	26
Recurring [Member] \| Investments in guaranteed income fund [Member]
Assets:
Investments	1,846	2,036
Recurring [Member] \| Investments - Mutual funds and other [Member]
Assets:
Investments		10,033
Recurring [Member] \| Total Investments [Member]
Assets:
Investments	$ 9,895	12,095
Recurring [Member] \| Mark To Market Energy Assets incl. natural gas and swap agreements[Member]
Assets:
Derivative assets		$ 7,076

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value, after the 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 not subject to a master netting arrangement and not elected to be offset.

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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 amount as of the balance sheet date of the asset arising from energy trading activities that involves the purchase and sale of energy under forward contracts at fixed and variable prices and the buying and selling of financial energy contracts that include exchange futures and options and over the counter options and swaps, which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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