Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets:
Investments	$ 3,098	$ 4,168
Mark-to-market energy assets, including put option	169
Quoted Prices in Active Markets (Level 1) | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities		0
Significant Other Observable Inputs (Level 2) | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	127	331
Significant Unobservable Inputs (Level 3) | Mark-to-market energy liabilities
Assets:
Mark-to-market energy assets, including put option	0
Liabilities:
Mark-to-market energy liabilities		0
Investments - other | Quoted Prices in Active Markets (Level 1)
Assets:
Investments	2,640	2,161
Investments - other | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Investments - other | Significant Unobservable Inputs (Level 3)
Assets:
Investments	0	0
Investments in equity securities
Assets:
Investments	0	2,013
Investments in equity securities | Quoted Prices in Active Markets (Level 1)
Assets:
Investments	0	2,007
Investments in equity securities | Significant Other Observable Inputs (Level 2)
Assets:
Investments	0	0
Investments in equity securities | Significant Unobservable Inputs (Level 3)
Assets:
Investments	458	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	385	210
Mark-to-market energy assets, including put option | Significant Unobservable Inputs (Level 3)
Assets:
Mark-to-market energy assets, including put option		0
Fair Value | Mark-to-market energy liabilities
Liabilities:
Mark-to-market energy liabilities	127	331
Fair Value | Investments - other
Assets:
Investments	2,640	2,161
Fair Value | Investments in equity securities
Assets:
Investments	458	2,007
Fair Value | Mark-to-market energy assets, including put option
Assets:
Mark-to-market energy assets, including put option	$ 385	$ 210