Shareholders' Equity (Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 27, 2017	Dec. 28, 2016	Dec. 30, 2015
Equity, Class of Treasury Stock [Line Items]
Common stock shares repurchased during the period (shares)	6,800	4,580	8,500
Common stock shares repurchased during the period (value in US$)	$ 82,858	$ 51,771	$ 92,676
Share Repurchase Program 2017 [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase, authorized amount (dollars)	200,000
Remaining shares to be repurchased (value in US$)	196,300
Share Repurchase Program 2016 [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase, authorized amount (dollars)	100,000
Share Repurchase Program 2015 [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase, authorized amount (dollars)	$ 100,000
November 2015 Accelerated Share Repurchase [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase, authorized amount (dollars)			$ 50,000
Common stock shares repurchased during the period (shares)		1,500	3,500
Volume-weighted average price		$ 9.90
Common stock shares repurchased during the period (value in US$)		$ 13,100	$ 36,900
Remaining shares to be repurchased (value in US$)			$ 13,100
November 2016 Accelerated Share Repurchase [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase, authorized amount (dollars)		$ 25,000
Common stock shares repurchased during the period (shares)	500	1,500
Volume-weighted average price	$ 12.36
Common stock shares repurchased during the period (value in US$)	$ 6,900	$ 18,100
Remaining shares to be repurchased (value in US$)		$ 6,900