Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Total
Balance, at Dec. 31, 2016	$ 9,949	$ 1,062,778	$ 4,852	$ (150,857)	$ 926,722
Balance, shares at Dec. 31, 2016	33,047,807			6,149,364
Net income		34,760			34,760
Other comprehensive income (loss), net of reclassification adjustments and tax			150		150
Dividends paid		(24,209)			(24,209)
Balance, at Sep. 30, 2017	$ 9,949	1,073,330	5,002	$ (150,857)	937,424
Balance, shares at Sep. 30, 2017	33,047,807			6,149,364
Cumulative effect of accounting priciple adoption of ASU 2016-01		5,482	(5,482)
Balance, at Dec. 30, 2017	$ 9,949	1,127,872	5,880	$ (150,857)	992,844
Balance, shares at Dec. 30, 2017	33,047,807			6,149,364
Net income		49,492			49,492
Other comprehensive income (loss), net of reclassification adjustments and tax			(581)		(581)
Dividends paid		(24,209)			(24,209)
Balance, at Sep. 29, 2018	$ 9,949	$ 1,158,636	$ (183)	$ (150,857)	$ 1,017,545
Balance, shares at Sep. 29, 2018	33,047,807			6,149,364