Schedule of Other Liabilities and Deferred Credits (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Deferred Credits and Other Liabilities [Abstract]
Postretirement benefits liability	$ 2,420	$ 2,642
Pension liabilities	36,526	36,614
Deferred supplemental savings plan liability	5,277	6,592
Other	13,462	12,728
Other liabilities and deferred credits	$ 57,685	$ 58,576

Amount of liability, recognized in statement of financial position, for defined benefit other postretirement plan, classified as noncurrent. Excludes pension plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant