Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2014
Summary Of Significant Accounting Policies [Line Items]
Equity method investments				$ 0
Net brokered margin gain (loss)	$ (2,700,000)	$ 9,400,000	$ (5,700,000)
Allowance for doubtful accounts on accounts receivable	4,994,000	2,719,000
Bad debt expense	2,300,000	250,000	$ 250,000
Inventory, other	33,217,000	17,854,000
Materials and supplies inventory
Summary Of Significant Accounting Policies [Line Items]
Inventory, other	20,800,000	11,800,000
Commodity inventory
Summary Of Significant Accounting Policies [Line Items]
Inventory, other	$ 4,800,000	$ 2,000,000