Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Investments	$ 3,542	$ 3,098
Quoted Prices in Active Markets (Level 1) [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities	0	0
Quoted Prices in Active Markets (Level 1) [Member] | Investments in equity securities [Member]
Assets:
Investments		0
Quoted Prices in Active Markets (Level 1) [Member] | Investments - other [Member]
Assets:
Investments		2,640
Quoted Prices in Active Markets (Level 1) [Member] | Mark To Market Energy Assets Including Put Option [Member]
Assets:
Mark-to-market energy assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities	32	127
Significant Other Observable Inputs (Level 2) [Member] | Investments in equity securities [Member]
Assets:
Investments		0
Significant Other Observable Inputs (Level 2) [Member] | Investments - other [Member]
Assets:
Investments		0
Significant Other Observable Inputs (Level 2) [Member] | Mark To Market Energy Assets Including Put Option [Member]
Assets:
Mark-to-market energy assets	136	385
Significant Unobservable Inputs (Level 3) [Member] | Mark-to-market energy liabilities [Member]
Assets:
Mark-to-market energy assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Investments in equity securities [Member]
Assets:
Investments		458
Significant Unobservable Inputs (Level 3) [Member] | Investments - other [Member]
Assets:
Investments		0
Recurring [Member] | Mark-to-market energy liabilities [Member]
Liabilities:
Mark-to-market energy liabilities	32	127
Recurring [Member] | Investments in equity securities [Member]
Assets:
Investments		458
Recurring [Member] | Investments - other [Member]
Assets:
Investments		2,640
Recurring [Member] | Mark To Market Energy Assets Including Put Option [Member]
Assets:
Mark-to-market energy assets	136	385
Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	410
Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Investments - other [Member]
Assets:
Investments	3,132
Recurring [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	0
Recurring [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Investments - other [Member]
Assets:
Investments	3,132
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	0
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Investments - other [Member]
Assets:
Investments	0
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Investments in guaranteed income fund [Member]
Assets:
Investments	410
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Investments - other [Member]
Assets:
Investments	$ 0