Discontinued Operations Income (Loss) Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net Sales									$ 0	$ 4,964	$ 22,794
Operating earnings (loss)									(1,170)	(8,707)	(15,578)
Tax expense (benefit)									(1,835)	(1,396)	(312)
Income (loss) from discontinued operations	$ 2,802	$ (1,894)	$ (77)	$ (166)	$ (1,126)	$ (815)	$ (34)	$ (5,336)	665	(7,311)	(15,266)
Included in Operating Earnings (Loss):
Gain (loss) on net assets held for sale									(287)	(2,906)	(8,448)
Gain (loss) on sale of discontinued operations									2,404	793	0
Avionics & Controls
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net Sales									0	4,964	17,572
Operating earnings (loss)									(396)	(447)	1,350
Tax expense (benefit)									286	(470)	1,487
Income (loss) from discontinued operations									(682)	23	(137)
Included in Operating Earnings (Loss):
Gain (loss) on net assets held for sale									(287)	320	(2,457)
Gain (loss) on sale of discontinued operations									0	793
Sensors & Systems
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net Sales									0	0	0
Operating earnings (loss)									0	894	(379)
Tax expense (benefit)									0	0	(83)
Income (loss) from discontinued operations									0	894	(296)
Included in Operating Earnings (Loss):
Gain (loss) on net assets held for sale									0	0	0
Gain (loss) on sale of discontinued operations									0	0
Advanced Materials
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net Sales									0	0	5,222
Operating earnings (loss)									(632)	(8,259)	(15,761)
Tax expense (benefit)									(2,084)	(614)	(1,448)
Income (loss) from discontinued operations									1,452	(7,645)	(14,313)
Included in Operating Earnings (Loss):
Gain (loss) on net assets held for sale									0	(3,226)	(5,991)
Gain (loss) on sale of discontinued operations									2,404	0
Other
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net Sales									0	0	0
Operating earnings (loss)									(142)	(895)	(788)
Tax expense (benefit)									(37)	(312)	(268)
Income (loss) from discontinued operations									(105)	(583)	(520)
Included in Operating Earnings (Loss):
Gain (loss) on net assets held for sale									0	0	$ 0
Gain (loss) on sale of discontinued operations									$ 0	$ 0