Employee Benefit Plans And Other Postretirement Benefits (Schedule Of Expected Benefit Payments And Medicare Subsidy Receipts For Next Five Years And Thereafter) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 27, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan Assets [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Expected benefit payments in 2013		$ 77,310
Expected benefit payments in 2014		78,884
Expected benefit payments in 2015		80,877
Expected benefit payments in 2016		83,377
Expected benefit payments in 2017		86,533
Expected benefit payments in 2018-2022		497,276
SERPA Benefits [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Expected benefit payments in 2013		2,145
Expected benefit payments in 2014		2,215
Expected benefit payments in 2015		2,234
Expected benefit payments in 2016		2,683
Expected benefit payments in 2017		2,976
Expected benefit payments in 2018-2022		21,253
Postretirement Healthcare Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Contributions by Employer		23,937	$ 28,048
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Expected benefit payments in 2013		33,848
Expected benefit payments in 2014		33,160
Expected benefit payments in 2015		31,571
Expected benefit payments in 2016		29,975
Expected benefit payments in 2017		28,139
Expected benefit payments in 2018-2022		$ 129,295
Subsequent Event [Member] | Pension Plan Assets [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Contributions by Employer	$ 25,000