Shareholders' Equity (Share Repurchase) (Details) - USD ($) shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 26, 2018	Dec. 27, 2017
Equity, Class of Treasury Stock [Line Items]
Purchase of treasury stock	$ 37,407
Number of accumulated shares repurchased (in shares)	45,588	43,151
Share Repurchase Program 2017 [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase, authorized amount (in dollars)	$ 200,000
Purchase of treasury stock (in shares)	2,400
Purchase of treasury stock	$ 37,400
Number of accumulated shares repurchased (in shares)	2,700
Value of shares repurchased	$ 41,100
Remaining shares to be repurchased (in dollars)	$ 158,900