Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Assets:
Investments	$ 4,168,000	$ 3,918,000
Quoted Prices in Active Markets (Level 1) [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities
Significant Other Observable Inputs (Level 2) [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities	331,000	1,496,000
Significant Unobservable Inputs (Level 3) [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities
Investments - other [Member]
Assets:
Investments		40,000
Investments - other [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Investments	2,161,000	1,734,000
Investments - other [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investments
Investments - other [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investments
Investments in equity securities [Member]
Assets:
Investments	2,013,000	2,294,000
Investments in equity securities [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Investments	2,007,000	2,224,000
Investments in equity securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Investments
Investments in equity securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Investments
Mark-to-market energy assets, including put option [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Mark-to-market energy assets, including put option
Mark-to-market energy assets, including put option [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Mark-to-market energy assets, including put option	210,000	1,754,000
Mark-to-market energy assets, including put option [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Mark-to-market energy assets, including put option
Fair Value [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities	331,000	1,496,000
Fair Value [Member] | Investments - other [Member]
Assets:
Investments	2,161,000	1,734,000
Fair Value [Member] | Investments in equity securities [Member]
Assets:
Investments	2,007,000	2,224,000
Fair Value [Member] | Mark-to-market energy assets, including put option [Member]
Assets:
Mark-to-market energy assets, including put option	$ 210,000	$ 1,754,000