Consolidated Statement of Changes in Stockholders' Equity - USD ($)	Common Stock Including Additional Paid in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Sep. 26, 2015	18,676,000
Balance at Sep. 26, 2015	$ 31,653,000	$ (10,897,000)	$ 579,163,000	$ 599,919,000
Issuance of common stock upon exercise of stock options (in shares)	120,000
Issuance of common stock upon exercise of stock options	$ 5,249,000			5,249,000
Issuance of common stock for employee stock purchase plan (in shares)	14,000
Issuance of common stock for employee stock purchase plan	$ 1,320,000			1,320,000
Foreign currency translation adjustment		(3,065,000)		(3,065,000)
Unrealized holding gain on marketable securities		547,000		547,000
Issuance of common stock under deferred stock plan	7,000			7,000
Dividends declared			(29,081,000)	(29,081,000)
Share-based compensation	$ 2,368,000			$ 2,368,000
Repurchase of common stock (in shares)	(142,000)			(141,700)
Repurchase of common stock	$ (15,265,000)			$ (15,265,019)
Net earnings			75,975,000	75,975,000
Balance (in shares) at Sep. 24, 2016	18,668,000
Balance at Sep. 24, 2016	$ 25,332,000	(13,415,000)	626,057,000	637,974,000
Issuance of common stock upon exercise of stock options (in shares)	124,000
Issuance of common stock upon exercise of stock options	$ 5,826,000			5,826,000
Issuance of common stock for employee stock purchase plan (in shares)	13,000
Issuance of common stock for employee stock purchase plan	$ 1,405,000			1,405,000
Foreign currency translation adjustment		3,745,000		3,745,000
Unrealized holding gain on marketable securities		795,000		795,000
Issuance of common stock under deferred stock plan	94,000			94,000
Dividends declared			(31,416,000)	(31,416,000)
Share-based compensation	$ 2,954,000			$ 2,954,000
Repurchase of common stock (in shares)	(143,000)			(142,665)
Repurchase of common stock	$ (18,229,000)			$ (18,228,763)
Net earnings			79,174,000	$ 79,174,000
Issuance of common stock under deferred stock plan (in shares)	1,000
Balance (in shares) at Sep. 30, 2017	18,663,000			18,663,000
Balance at Sep. 30, 2017	$ 17,382,000	(8,875,000)	673,815,000	$ 682,322,000
Issuance of common stock upon exercise of stock options (in shares)	98,000
Issuance of common stock upon exercise of stock options	$ 7,371,000			7,371,000
Issuance of common stock for employee stock purchase plan (in shares)	13,000
Issuance of common stock for employee stock purchase plan	$ 1,523,000			1,523,000
Foreign currency translation adjustment		(2,738,000)		(2,738,000)
Unrealized holding gain on marketable securities		(381,000)		(381,000)
Issuance of common stock under deferred stock plan	97,000			97,000
Dividends declared			(33,666,000)	(33,666,000)
Share-based compensation	$ 3,761,000			$ 3,761,000
Repurchase of common stock (in shares)	(21,000)			(20,604)
Repurchase of common stock	$ (2,794,000)			$ (2,794,027)
Net earnings			103,596,000	$ 103,596,000
Issuance of common stock under deferred stock plan (in shares)	1,000
Balance (in shares) at Sep. 29, 2018	18,754,000			18,754,000
Balance at Sep. 29, 2018	$ 27,340,000	$ (11,994,000)	$ 743,745,000	$ 759,091,000