Restructuring and Impairment Charges - Summary of Impairment and Restructuring Charges (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment charges	$ 4,000	$ 1,891
Wheeling Plant [Member]
Restructuring Cost and Reserve [Line Items]
Impairment of tangible assets	328	361
Restructuring charges and contract costs	1,749	3,275
Restructuring and impairment charges	2,077	3,636
Reserve beginning balance		2,290
Charges		3,636
Paid in 2016		(4,051)
Reserve ending balance	1,875	1,875
Wheeling Plant [Member] \| Severance and Other Employee Costs [Member]
Restructuring Cost and Reserve [Line Items]
Reserve beginning balance		445
Charges		869
Paid in 2016		(1,298)
Reserve ending balance	16	16
Wheeling Plant [Member] \| Site Closure and Other Associated Cost [Member]
Restructuring Cost and Reserve [Line Items]
Reserve beginning balance		1,845
Charges		2,767
Paid in 2016		(2,753)
Reserve ending balance	$ 1,859	$ 1,859

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
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-Section 50
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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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