CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 25, 2017	Jun. 26, 2016	Jun. 25, 2017	Jun. 26, 2016
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS
Unamortized net loss and other components of benefit plans, taxes	$ (1,714)	$ (1,535)	$ (3,428)	$ (3,070)
Other comprehensive loss, taxes	$ (2,649)	$ (252)	$ (2,697)	$ 78

Amount of tax (expense) benefit, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans, attributable to parent entity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=64809438&loc=SL4573702-111684

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569616-111683

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569643-111683

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration