Revenue (Impact of ASC 606 Adoption) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 30, 2017	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 892,518	$ 778,032	$ 787,955
Cost of sales	563,588	472,503	485,677
Gross profit	328,930	305,529	302,278
Selling and marketing	131,639	126,333	124,912
Income tax provision (benefit)	5,546	(17,105)	(2,073)
Net income	43,067	61,328	$ 25,084
Assets
Accounts receivable, net	121,260	122,243		$ 117,762
Unbilled accounts receivable, net	80,331	70,474		62,472
Inventories, net	167,199	139,109		155,836
Prepaid expenses and other current assets	23,761	24,572		29,223
Other long-term assets	3,553	2,263		3,323
Deferred income taxes	7,229	3,249		3,892
Liabilities and Shareholders' Equity
Advance payments from customers	70,520	80,131		93,699
Other accrued liabilities	43,165	19,146		16,642
Deferred income taxes	41,531	46,482		45,254
Other long-term liabilities	15,164	4,894		11,883
Accumulated other comprehensive income (loss)	(18,473)	1,476
Retained earnings	315,329	300,585		$ 294,358
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	849,805
Cost of sales	535,204
Gross profit	314,601
Selling and marketing	129,894
Income tax provision (benefit)	3,399
Net income	32,630
Assets
Accounts receivable, net	120,496
Unbilled accounts receivable, net	70,949
Inventories, net	166,668
Prepaid expenses and other current assets	20,328
Other long-term assets	2,690
Deferred income taxes	7,538
Liabilities and Shareholders' Equity
Advance payments from customers	74,209
Other accrued liabilities	28,506
Deferred income taxes	41,548
Other long-term liabilities	15,715
Accumulated other comprehensive income (loss)	(18,525)
Retained earnings	311,119
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	42,713
Cost of sales	28,384
Gross profit	14,329
Selling and marketing	1,745
Income tax provision (benefit)	2,147
Net income	10,437
Assets
Accounts receivable, net	764	(4,481)
Unbilled accounts receivable, net	9,382	(8,002)
Inventories, net	531	16,727
Prepaid expenses and other current assets	3,433	4,651
Other long-term assets	863	1,060
Deferred income taxes	(309)	643
Liabilities and Shareholders' Equity
Advance payments from customers	(3,689)	13,568
Other accrued liabilities	14,659	(2,504)
Deferred income taxes	(17)	(1,228)
Other long-term liabilities	(551)	6,989
Accumulated other comprehensive income (loss)	52
Retained earnings	$ 4,210	$ (6,227)