CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (15,578)	$ (29,041)	$ 101,946	$ 119,694
Other comprehensive income:
Amortization of net actuarial losses and prior service credits into earnings	541	552	1,623	1,656
Recognition in earnings of net actuarial loss for pension settlement	900	0	900	0
Other comprehensive income	1,441	552	2,523	1,656
Total comprehensive (loss) income	$ (14,137)	$ (28,489)	$ 104,469	$ 121,350