Revenue (Impact of ASC 606 Adoption) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018	Sep. 30, 2018	Sep. 29, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 232,209	$ 194,668	$ 668,436	$ 580,153
Cost of sales	147,106	118,384	417,678	351,116
Gross profit	85,103	76,284	250,758	229,037
Selling and marketing	33,321	32,171	98,805	94,796
Income tax provision (benefit)	2,605	1,066	6,217	(20,877)
Net income	13,585	$ 8,979	38,246	$ 50,568
Assets
Accounts receivable, net	131,365		131,365		$ 117,762	$ 122,243
Unbilled accounts receivable, net	68,804		68,804		62,472	70,474
Inventories, net	164,853		164,853		155,836	139,109
Prepaid expenses and other current assets	27,118		27,118		29,223	24,572
Other long-term assets	3,986		3,986		3,323	2,263
Deferred income taxes	3,818		3,818		3,892	3,249
Liabilities and Shareholders' Equity
Advance payments from customers	87,935		87,935		93,699	80,131
Accrued income taxes	3,736		3,736			4,928
Other accrued liabilities	35,367		35,367		16,642	19,146
Deferred income taxes	50,315		50,315		45,254	46,482
Other long-term liabilities	15,305		15,305		11,883	4,894
Accumulated other comprehensive income (loss)	(5,409)		(5,409)			1,476
Retained earnings	316,249		316,249		$ 294,358	300,585
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	213,443		636,546
Cost of sales	136,563		397,295
Gross profit	76,880		239,251
Selling and marketing	33,075		98,566
Income tax provision (benefit)	1,326		4,363
Net income	6,887		28,832
Assets
Accounts receivable, net	133,548		133,548
Unbilled accounts receivable, net	59,784		59,784
Inventories, net	156,108		156,108
Prepaid expenses and other current assets	24,003		24,003
Other long-term assets	2,880		2,880
Deferred income taxes	3,167		3,167
Liabilities and Shareholders' Equity
Advance payments from customers	84,970		84,970
Accrued income taxes	3,345		3,345
Other accrued liabilities	20,566		20,566
Deferred income taxes	51,540		51,540
Other long-term liabilities	15,021		15,021
Accumulated other comprehensive income (loss)	(5,460)		(5,460)
Retained earnings	313,062		313,062
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	18,766		31,890
Cost of sales	10,543		20,383
Gross profit	8,223		11,507
Selling and marketing	246		239
Income tax provision (benefit)	1,279		1,854
Net income	6,698		9,414
Assets
Accounts receivable, net	(2,183)		(2,183)			(4,481)
Unbilled accounts receivable, net	9,020		9,020			(8,002)
Inventories, net	8,745		8,745			16,727
Prepaid expenses and other current assets	3,115		3,115			4,651
Other long-term assets	1,106		1,106			1,060
Deferred income taxes	651		651			643
Liabilities and Shareholders' Equity
Advance payments from customers	2,965		2,965			13,568
Accrued income taxes	391		391
Other accrued liabilities	14,801		14,801			(2,504)
Deferred income taxes	(1,225)		(1,225)			(1,228)
Other long-term liabilities	284		284			6,989
Accumulated other comprehensive income (loss)	51		51
Retained earnings	$ 3,187		$ 3,187			$ (6,227)