Defined Benefit Plans - Fair value of pension plan assets (Details) - USD ($) $ in Thousands	Oct. 03, 2020	Sep. 28, 2019	Sep. 29, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 12,901	$ 12,997	$ 12,486
Small cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50	135
Mid cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	143	250
Large cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	293	751
Total market stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,140	1,689
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,166	1,276
Emerging markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	197	204
Bonds and mortgages
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,323	3,110
Inflation protected
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	634
High yield
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	272	634
Liability driven investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,848	3,811
Money market
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	469	503
(Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	469	503
(Level 1) | Small cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Mid cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Large cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Total market stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Emerging markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Bonds and mortgages
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Inflation protected
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | High yield
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Liability driven investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 1) | Money market
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	469	503
(Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12,432	12,494
(Level 2) | Small cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50	135
(Level 2) | Mid cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	143	250
(Level 2) | Large cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	293	751
(Level 2) | Total market stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,140	1,689
(Level 2) | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,166	1,276
(Level 2) | Emerging markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	197	204
(Level 2) | Bonds and mortgages
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,323	3,110
(Level 2) | Inflation protected
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	634
(Level 2) | High yield
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	272	634
(Level 2) | Liability driven investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,848	3,811
(Level 2) | Money market
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Small cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Mid cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Large cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Total market stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Emerging markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Bonds and mortgages
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Inflation protected
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | High yield
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Liability driven investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
(Level 3) | Money market
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0