Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Assets:
Investments	$ 13,620	$ 12,282
Energy Marketing Contracts Assets, Current	1,180	1,027
Liabilities:
Energy Marketing Contract Liabilities, Current	27	354
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Assets, Fair Value Disclosure	12,225	10,793
Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member]
Assets:
Investments	21	21
Quoted Prices in Active Markets (Level 1) [Member] | Investments - Mutual funds and other [Member]
Assets:
Investments	12,204	10,772
Quoted Prices in Active Markets (Level 1) [Member] | Total Investments [Member]
Assets:
Investments	12,225	10,793
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, Fair Value Disclosure	1,372	1,067
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, Fair Value Disclosure	1,395	1,489
Significant Unobservable Inputs (Level 3) [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	1,395	1,489
Significant Unobservable Inputs (Level 3) [Member] | Total Investments [Member]
Assets:
Investments	1,395	1,489
Recurring [Member]
Assets:
Assets, Fair Value Disclosure	14,992	13,349
Liabilities:
Energy Marketing Contract Liabilities, Current		1,281
Recurring [Member] | Equity Securities [Member]
Assets:
Investments	21	21
Recurring [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	1,395	1,489
Recurring [Member] | Investments - Mutual funds and other [Member]
Assets:
Investments		10,772
Recurring [Member] | Total Investments [Member]
Assets:
Investments	13,620	12,282
Recurring [Member] | Mark To Market Energy Assets incl. natural gas and swap agreements[Member]
Assets:
Derivative assets	$ 1,372	$ 1,067