Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

Name:	us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Pension and Other Postretirement Benefit Plans - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Mar. 27, 2020	Mar. 29, 2019	Dec. 28, 2018	Mar. 27, 2020	Mar. 29, 2019
Defined Benefit Plan Disclosure [Line Items]
Settlement gain (loss)	$ 0	$ 32,449		$ (2,651)	$ 34,621
CH2M Hill and OMI Retiree Medical Plans
Defined Benefit Plan Disclosure [Line Items]
Settlement gain (loss)		$ 32,400	$ 2,200