Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Assets:
Investments	$ 14,156	$ 12,282
Energy Marketing Contracts Assets, Current	405	1,027
Liabilities:
Energy Marketing Contract Liabilities, Current	633	354
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Assets, Fair Value Disclosure	13,039	10,793
Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member]
Assets:
Investments	23	21
Quoted Prices in Active Markets (Level 1) [Member] | Investments - Mutual funds and other [Member]
Assets:
Investments	13,016	10,772
Quoted Prices in Active Markets (Level 1) [Member] | Total Investments [Member]
Assets:
Investments	13,039	10,793
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, Fair Value Disclosure	527	1,067
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, Fair Value Disclosure	1,116	1,489
Significant Unobservable Inputs (Level 3) [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	1,116	1,489
Significant Unobservable Inputs (Level 3) [Member] | Total Investments [Member]
Assets:
Investments	1,116	1,489
Recurring [Member]
Assets:
Assets, Fair Value Disclosure	14,682	13,349
Liabilities:
Energy Marketing Contract Liabilities, Current		1,281
Recurring [Member] | Equity Securities [Member]
Assets:
Investments	23	21
Recurring [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	1,116	1,489
Recurring [Member] | Investments - Mutual funds and other [Member]
Assets:
Investments		10,772
Recurring [Member] | Total Investments [Member]
Assets:
Investments	14,155	12,282
Recurring [Member] | Mark To Market Energy Assets incl. natural gas and swap agreements[Member]
Assets:
Derivative assets	$ 527	$ 1,067