Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Assets:
Investments	$ 3,678,000	$ 3,098,000
Quoted Prices in Active Markets (Level 1) | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	0	0
Significant Other Observable Inputs (Level 2) | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	1,018,000	127,000
Significant Unobservable Inputs (Level 3) | Mark-to-market energy liabilities
Assets:
Mark-to-market energy assets, including put option	0	0
Guaranteed Income Fund [Member] | Quoted Prices in Active Markets (Level 1)
Assets:
Investments	0
Guaranteed Income Fund [Member] | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0
Guaranteed Income Fund [Member] | Significant Unobservable Inputs (Level 3)
Assets:
Investments	287,000	458,000
Investments - other | Quoted Prices in Active Markets (Level 1)
Assets:
Investments	3,391,000	2,640,000
Investments - other | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0
Investments - other | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0
Mark-to-market energy assets, including put option | Quoted Prices in Active Markets (Level 1)
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	1,055,000	385,000
Fair Value | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	1,018,000	127,000
Fair Value | Guaranteed Income Fund [Member]
Assets:
Investments	287,000	458,000
Fair Value | Investments - other
Assets:
Investments	3,391,000	2,640,000
Fair Value | Mark-to-market energy assets, including put option
Assets:
Mark-to-market energy assets, including put option	$ 1,055,000	$ 385,000