Retirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands				3 Months Ended		4 Months Ended	6 Months Ended		12 Months Ended
		Mar. 31, 2020	Dec. 31, 2019	Apr. 12, 2020	Apr. 14, 2019	Jan. 19, 2020	Apr. 12, 2020	Apr. 14, 2019	Sep. 29, 2019
Defined Benefit Plan Disclosure [Line Items]
Pension settlements				$ (300)		$ (38,600)
Return on asset assumption (percent)		5.20%	5.90%						5.80%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost				3,669	$ 5,286		$ 8,745	$ 12,334
Expected return on plan assets				(4,706)	(6,077)		(11,362)	(14,181)
Pension settlements				321	0		38,927	0
Actuarial loss (gain)	[1]			1,019	913		2,691	2,132
Amortization of unrecognized prior service cost	[1]			19	27		45	62
Net periodic benefit cost				322	149		39,046	347
Postretirement Healthcare Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost				187	230		435	537
Actuarial loss (gain)	[1]			3	(36)		9	(85)
Net periodic benefit cost				$ 190	$ 194		$ 444	$ 452

[1] Amounts were reclassified from accumulated OCI into net earnings as a component of “Other pension and post-retirement expenses, net