Revenue (Impact of ASC 606 Adoption) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 29, 2018	Dec. 30, 2017	Sep. 30, 2018	Sep. 29, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 203,181	$ 194,162
Cost of sales	124,876	116,234
Gross profit	78,305	77,928
Selling and marketing	32,089	32,028
Income tax provision (benefit)	696	(23,681)
Net income	10,501	$ 33,151
Assets
Accounts receivable, net	115,384		$ 117,762	$ 122,243
Unbilled accounts receivable, net	60,656		62,472	70,474
Inventories, net	183,465		155,836	139,109
Prepaid expenses and other current assets	30,085		29,223	24,572
Other long-term assets	3,841		3,323	2,263
Deferred income taxes	4,501		3,892	3,249
Liabilities and Shareholders' Equity
Advance payments from customers	101,367		93,699	80,131
Accrued income taxes	4,853			4,928
Other accrued liabilities	26,623		16,642	19,146
Deferred income taxes	50,846		45,254	46,482
Other long-term liabilities	12,623		11,883	4,894
Accumulated other comprehensive income (loss)	(3,691)			1,476
Retained earnings	299,493		$ 294,358	300,585
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	198,438
Cost of sales	120,420
Gross profit	78,018
Selling and marketing	32,252
Income tax provision (benefit)	615
Net income	10,132
Assets
Accounts receivable, net	123,814
Unbilled accounts receivable, net	59,901
Inventories, net	164,298
Prepaid expenses and other current assets	25,933
Other long-term assets	2,845
Deferred income taxes	3,856
Liabilities and Shareholders' Equity
Advance payments from customers	87,148
Accrued income taxes	5,196
Other accrued liabilities	17,891
Deferred income taxes	52,074
Other long-term liabilities	10,871
Accumulated other comprehensive income (loss)	(3,702)
Retained earnings	305,351
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	4,743
Cost of sales	4,456
Gross profit	287
Selling and marketing	(163)
Income tax provision (benefit)	81
Net income	369
Assets
Accounts receivable, net	(8,430)			(4,481)
Unbilled accounts receivable, net	755			(8,002)
Inventories, net	19,167			16,727
Prepaid expenses and other current assets	4,152			4,651
Other long-term assets	996			1,060
Deferred income taxes	645			643
Liabilities and Shareholders' Equity
Advance payments from customers	14,219			13,568
Accrued income taxes	(343)
Other accrued liabilities	8,732			(2,504)
Deferred income taxes	(1,228)			(1,228)
Other long-term liabilities	1,752			6,989
Accumulated other comprehensive income (loss)	11
Retained earnings	$ (5,858)			$ (6,227)