Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock Including Additional Paid in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Sep. 30, 2017	18,663
Balance at Sep. 30, 2017	$ 17,382	$ (8,875)	$ 673,815	$ 682,322
Issuance of common stock upon exercise of stock options (in shares)	5
Issuance of common stock upon exercise of stock options	$ 253	0	0	253
Foreign currency translation adjustment	0	(3,887)	0	(3,887)
Dividends declared	0	0	(8,400)	(8,400)
Share-based compensation	952	0	0	952
Repurchase of common stock	0	0	0	0
Net Earnings	0	0	36,249	36,249
Issuance of common stock under deferred stock plan	2	0	0	2
Unrealized holding loss on marketable securities	$ 0	(110)	0	(110)
Balance (in shares) at Dec. 30, 2017	18,668
Balance at Dec. 30, 2017	$ 18,589	(12,872)	701,664	707,381
Balance (in shares) at Sep. 30, 2017	18,663
Balance at Sep. 30, 2017	$ 17,382	(8,875)	673,815	682,322
Foreign currency translation adjustment				(4,348)
Net Earnings				80,211
Balance (in shares) at Jun. 30, 2018	18,705
Balance at Jun. 30, 2018	$ 23,047	(13,770)	728,798	738,075
Balance (in shares) at Dec. 30, 2017	18,668
Balance at Dec. 30, 2017	$ 18,589	(12,872)	701,664	707,381
Issuance of common stock upon exercise of stock options (in shares)	21
Issuance of common stock upon exercise of stock options	$ 1,951	0	0	1,951
Foreign currency translation adjustment	0	1,898	0	1,898
Dividends declared	0	0	(8,413)	(8,413)
Share-based compensation	868	0	0	868
Repurchase of common stock	0	0	0	0
Net Earnings	$ 0	0	17,833	17,833
Issuance of common stock for employee stock purchase plan (in shares)	7
Issuance of common stock for employee stock purchase plan	$ 756	0	0	756
Issuance of common stock under deferred stock plan (in shares)	1
Issuance of common stock under deferred stock plan	$ 92	0	0	92
Unrealized holding loss on marketable securities	$ 0	(184)	0	(184)
Balance (in shares) at Mar. 31, 2018	18,697
Balance at Mar. 31, 2018	$ 22,256	(11,158)	711,084	722,182
Issuance of common stock upon exercise of stock options (in shares)	29
Issuance of common stock upon exercise of stock options	$ 2,601	0	0	2,601
Foreign currency translation adjustment	0	(2,359)	0	(2,359)
Dividends declared	0	0	(8,415)	(8,415)
Share-based compensation	982	0	0	982
Repurchase of common stock	(2,794)	0	0	(2,794)
Net Earnings	0	0	26,129	26,129
Issuance of common stock under deferred stock plan	2	0	0	2
Unrealized holding loss on marketable securities	$ 0	(253)	0	(253)
Repurchase of common stock (in shares)	(21)
Balance (in shares) at Jun. 30, 2018	18,705
Balance at Jun. 30, 2018	$ 23,047	(13,770)	728,798	$ 738,075
Balance (in shares) at Sep. 29, 2018	18,754			18,754,000
Balance at Sep. 29, 2018	$ 27,340	(11,994)	743,745	$ 759,091
Issuance of common stock upon exercise of stock options (in shares)	20
Issuance of common stock upon exercise of stock options	$ 1,704	0	0	1,704
Foreign currency translation adjustment	0	(1,359)	0	(1,359)
Reclass from accumulated other comprehensive gain | Accounting Standards Update 2016-01 [Member]	0	(85)	85	0
Dividends declared	0	0	(9,389)	(9,389)
Share-based compensation	972	0	0	972
Repurchase of common stock	0	0	0	0
Net Earnings	$ 0	0	17,526	17,526
Balance (in shares) at Dec. 29, 2018	18,774
Balance at Dec. 29, 2018	$ 30,016	(13,438)	751,967	$ 768,545
Balance (in shares) at Sep. 29, 2018	18,754			18,754,000
Balance at Sep. 29, 2018	$ 27,340	(11,994)	743,745	$ 759,091
Foreign currency translation adjustment				(469)
Net Earnings				$ 68,752
Balance (in shares) at Jun. 29, 2019	18,830			18,830,000
Balance at Jun. 29, 2019	$ 37,840	(12,548)	784,375	$ 809,667
Balance (in shares) at Dec. 29, 2018	18,774
Balance at Dec. 29, 2018	$ 30,016	(13,438)	751,967	768,545
Issuance of common stock upon exercise of stock options (in shares)	34
Issuance of common stock upon exercise of stock options	$ 3,451	0	0	3,451
Foreign currency translation adjustment	0	394	0	394
Dividends declared	0	0	(9,405)	(9,405)
Share-based compensation	914	0	0	914
Repurchase of common stock	0	0	0	0
Net Earnings	$ 0	0	20,354	20,354
Issuance of common stock for employee stock purchase plan (in shares)	6
Issuance of common stock for employee stock purchase plan	$ 772	0	0	772
Issuance of common stock under deferred stock plan (in shares)	1
Issuance of common stock under deferred stock plan	$ 90	0	0	90
Balance (in shares) at Mar. 30, 2019	18,815
Balance at Mar. 30, 2019	$ 35,243	(13,044)	762,916	785,115
Issuance of common stock upon exercise of stock options (in shares)	15
Issuance of common stock upon exercise of stock options	$ 1,499	0	0	1,499
Foreign currency translation adjustment	0	496	0	496
Dividends declared	0	0	(9,413)	(9,413)
Share-based compensation	1,098	0	0	1,098
Repurchase of common stock	0	0	0	0
Net Earnings	$ 0	0	30,872	$ 30,872
Balance (in shares) at Jun. 29, 2019	18,830			18,830,000
Balance at Jun. 29, 2019	$ 37,840	$ (12,548)	$ 784,375	$ 809,667