Retirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands					3 Months Ended			4 Months Ended	9 Months Ended		12 Months Ended
		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jul. 05, 2020	Apr. 12, 2020	Jul. 07, 2019	Jan. 19, 2020	Jul. 05, 2020	Jul. 07, 2019	Sep. 29, 2019
Defined Benefit Plan Disclosure [Line Items]
Pension settlements					$ (100)	$ (300)		$ (38,600)
Return on asset assumption (percent)		5.40%	5.20%	5.90%							5.80%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost					3,581		$ 5,286		$ 12,326	$ 17,619
Expected return on plan assets					(3,779)		(6,077)		(15,141)	(20,257)
Pension settlements					103		0		39,030	0
Actuarial loss (gain)	[1]				1,367		914		4,058	3,046
Amortization of unrecognized prior service cost	[1]				20		27		65	89
Net periodic benefit cost					1,292		150		40,338	497
Postretirement Healthcare Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost					186		229		621	766
Actuarial loss (gain)	[1]				4		(37)		13	(122)
Net periodic benefit cost					$ 190		$ 192		$ 634	$ 644

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