CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 26, 2019	Dec. 27, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Pension gain (loss) arising during period, net of tax effect (benefit)	$ (993)	$ (1,833)	$ 708
Amortization of the net actuarial loss and prior service credit related to the pension, net of tax effect	259	109	167
Fair market value adjustment of interest rate swap, net of tax benefit	335	300	115
Reclassification adjustment on interest rate swap included in interest expense, net of tax effect	$ 263	$ 44	$ 59

Amount of tax expense (benefit) for increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e640-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 45
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683

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Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.

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- Definition

Amount, before reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e640-108580

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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