CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 26, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 37,995	$ 14,440	$ 84,352
Other comprehensive income:
Net unrealized (losses) gains on cash flow hedges	(10)	6	(1,159)
Reclassification of realized losses on cash flow hedges into earnings	215	1,100	1,388
Amortization of net actuarial losses and prior service credits into earnings and net change in funded status of benefit plans	10,715	(55)	(5,207)
Recognition in earnings of net actuarial loss for pension settlement	6,100	2,000	2,000
Other comprehensive income (loss)	17,020	3,051	(2,978)
Total comprehensive income	$ 55,015	$ 17,491	$ 81,374