Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Assets:
Investments	$ 11,693	$ 10,576
Energy Marketing Contracts Assets, Current	1,704	2,787
Liabilities:
Energy Marketing Contract Liabilities, Current	2,178	585
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Assets, Fair Value Disclosure	9,937	8,723
Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member]
Assets:
Investments	23	24
Quoted Prices in Active Markets (Level 1) [Member] | Investments - Mutual funds and other [Member]
Assets:
Investments	9,914	8,699
Quoted Prices in Active Markets (Level 1) [Member] | Total Investments [Member]
Assets:
Investments	9,937	8,723
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets, Fair Value Disclosure	1,844	3,769
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Assets, Fair Value Disclosure	1,756	1,853
Significant Unobservable Inputs (Level 3) [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	1,756	1,853
Significant Unobservable Inputs (Level 3) [Member] | Total Investments [Member]
Assets:
Investments	1,756	1,853
Recurring [Member]
Assets:
Assets, Fair Value Disclosure	13,537	14,345
Liabilities:
Energy Marketing Contract Liabilities, Current		2,215
Recurring [Member] | Equity Securities [Member]
Assets:
Investments	23	24
Recurring [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	1,756	1,853
Recurring [Member] | Investments - Mutual funds and other [Member]
Assets:
Investments		8,699
Recurring [Member] | Total Investments [Member]
Assets:
Investments	11,693	10,576
Recurring [Member] | Mark To Market Energy Assets incl. natural gas and swap agreements[Member]
Assets:
Derivative assets	$ 1,844	$ 3,769