Reconciliation of Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Unrecognized tax benefits as of the beginning of year	$ 8,848	$ 7,877	$ 11,389
Gross increase due to prior-period adjustments	0	1,608	445
Gross decrease due to prior-period adjustments	(2,140)	0	(475)
Gross increase due to current-period adjustments	738	853	1,475
Gross decrease due to settlements with taxing authorities	(240)	0	(2,068)
Gross decrease due to a lapse of the statute of limitations	(1,122)	(1,490)	(2,889)
Total change in unrecognized gross benefit	(2,764)	971	(3,512)
Unrecognized tax benefits as of the end of the fiscal year	6,084	8,848	7,877
Unrecognized tax benefits that, if recognized, would impact the effective tax rate	5,240	4,888	6,626
Statement of operations:
Total amount of interest income (expense) included in income tax expense	(289)	33	(308)
Recognized in the statement of financial position:
Total amount of accrued interest included in income taxes payable	$ 326	$ 616	$ 583