Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets:
Investments	$ 12,282	$ 10,576
Fair Value, Inputs, Level 1 [Member]
Assets:
Assets, Fair Value Disclosure	10,793	8,723
Fair Value, Inputs, Level 1 [Member] | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Assets, Fair Value Disclosure	1,067	3,769
Significant Other Observable Inputs (Level 2) | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	1,281	2,215
Significant Unobservable Inputs (Level 3)
Assets:
Assets, Fair Value Disclosure	1,489	1,853
Significant Unobservable Inputs (Level 3) | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Investments	21	24
Equity Securities [Member] | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Equity Securities [Member] | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Guaranteed Income Fund [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Investments	0	0
Guaranteed Income Fund [Member] | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Guaranteed Income Fund [Member] | Significant Unobservable Inputs (Level 3)
Assets:
Investments	1,489	1,853
Other Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Investments	10,772	8,699
Other Investments [Member] | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Other Investments [Member] | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Investments	10,793	8,723
Investments [Member] | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Investments [Member] | Significant Unobservable Inputs (Level 3)
Assets:
Investments	1,489	1,853
Mark-to-market energy assets, including put option | Fair Value, Inputs, Level 1 [Member]
Assets:
Mark-to-market energy assets, including put option	0	0
Mark-to-market energy assets, including put option | Significant Other Observable Inputs (Level 2)
Assets:
Mark-to-market energy assets, including put option	1,067	3,769
Mark-to-market energy assets, including put option | Significant Unobservable Inputs (Level 3)
Assets:
Mark-to-market energy assets, including put option	0	0
Fair Value
Assets:
Assets, Fair Value Disclosure	13,349	14,345
Fair Value | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	1,281	2,215
Fair Value | Equity Securities [Member]
Assets:
Investments	21	24
Fair Value | Guaranteed Income Fund [Member]
Assets:
Investments	1,489	1,853
Fair Value | Other Investments [Member]
Assets:
Investments	10,772	8,699
Fair Value | Investments [Member]
Assets:
Investments	12,282	10,576
Fair Value | Mark-to-market energy assets, including put option
Assets:
Mark-to-market energy assets, including put option	$ 1,067	$ 3,769