Schedule of Amounts Recognized in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 29, 2017	Sep. 30, 2016
Amount Recognized in the Consolidated Balance Sheet
Non-current liability	$ (66,981)	$ (92,520)
Amounts Recognized in Accumulated Other Comprehensive Income
Ending balance	81,782	116,346
Pension Plan
Amount Recognized in the Consolidated Balance Sheet
Non-current asset	4,267	2,395
Current liability	(1,840)	(1,912)
Non-current liability	(54,108)	(80,000)
Net amount recognized	(51,681)	(79,517)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial loss (gain)	78,713	112,420
Prior service cost	2,593	2,951
Ending balance	81,306	115,371
Other Postretirement Benefit Plan
Amount Recognized in the Consolidated Balance Sheet
Non-current asset	0	0
Current liability	(669)	(716)
Non-current liability	(12,873)	(12,520)
Net amount recognized	(13,542)	(13,236)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial loss (gain)	476	975
Prior service cost	0	0
Ending balance	$ 476	$ 975