Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]
Brokered margin loss	$ 5,700,000
Allowance for doubtful accounts on accounts receivable	2,494,000	2,374,000
Bad Debt Expense	250,000	750,000	946,000
Liability due to insufficient reserves	482,000
Inventory, other	12,451,000	22,315,000
Materials and supplies inventory
Summary Of Significant Accounting Policies [Line Items]
Inventory, other	9,600,000	16,300,000
Commodity inventory
Summary Of Significant Accounting Policies [Line Items]
Inventory, other	$ 0	$ 2,600,000