Balance Sheet Items (Schedule Of Restructuring Costs) (Details) $ in Thousands	3 Months Ended	9 Months Ended	21 Months Ended
	Sep. 26, 2015 USD ($)	Sep. 26, 2015 USD ($) employee	Dec. 25, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of employees, reduction in force | employee		200
Employee severance and related compensation benefits	$ (70)	$ 13,015
Site closures and asset impairments	1,165	1,165
Total restructuring costs	1,095	14,180
Cost Of Revenues [Member]
Restructuring Cost and Reserve [Line Items]
Employee severance and related compensation benefits	(6)	1,158
Research And Development, Net [Member]
Restructuring Cost and Reserve [Line Items]
Employee severance and related compensation benefits	(80)	7,864
Selling, General And Administrative [Member]
Restructuring Cost and Reserve [Line Items]
Employee severance and related compensation benefits	$ 16	$ 3,993
Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Site closures and asset impairments			$ 2,000
Minimum [Member] | Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Employee severance and related compensation benefits			13,000
Total restructuring costs			15,000
Maximum [Member] | Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Employee severance and related compensation benefits			14,000
Total restructuring costs			$ 16,000