Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Jun. 16, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary Of Significant Accounting Policies [Line Items]
Income (Loss) from equity method investments	$ 0	$ (3,095,000)	$ 2,973,000	$ (5,670,000)
Brokered margin gain (loss)		9,400,000	(5,700,000)
Allowance for doubtful accounts on accounts receivable		2,719,000	2,494,000
Bad debt expense		250,000	250,000	750,000
Liability due to insufficient reserves		52,000
Inventory, other		17,854,000	12,451,000
Inventory, other		2,000,000	0
Materials and supplies inventory
Summary Of Significant Accounting Policies [Line Items]
Inventory, other		$ 11,800,000	$ 9,600,000