Quarterly Financial Data - Schedule of Quarterly Financial Information (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Quarterly Financial Data [Line Items]
Gross profit	$ 31,378	$ 24,386	$ 48,869	$ 48,722	$ 30,566	$ 48,909	$ 38,659	$ 25,422	$ 153,355	$ 143,556	$ 183,736
Income from continuing operations	718	(3,772)	11,134	11,643	37,473	10,250	7,486	(68)	19,723	55,141	58,786
Fees and Expenses Relating to Certain Activist Shareholders' Proposals [Member]
Schedule Of Quarterly Financial Data [Line Items]
Income from continuing operations				4,163
Interest Expense [Member]
Schedule Of Quarterly Financial Data [Line Items]
Income from continuing operations	4,141	5,079	5,671	6,708	7,324	5,395	536	731
Precious Metal Recovery [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit						4,493
Income from continuing operations						4,493
Business Interruption Insurance Recoveries [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit				22,836	10,203	4,227	3,400	10,810
Income from continuing operations				22,836	10,203	4,227	3,400	10,810
Undesignated Commodities Contracts [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit	(3,095)	(214)	(105)	2,216	31		(113)	(162)
Income from continuing operations	(3,095)	(214)	(105)	2,216	31		(113)	(162)
Turnaround Costs [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit	(105)	(5,215)	(840)	(330)	(2,112)	24	(1,398)	(1,587)
Income from continuing operations	(105)	(5,215)	(840)	(330)	(2,112)	24	(1,398)	(1,587)
Property Insurance Recoveries [Member]
Schedule Of Quarterly Financial Data [Line Items]
Income from continuing operations				$ 5,147	$ 66,000	$ 255