PENSION AND OTHER POSTRETIREMENT BENEFITS (Schedule of Defined Benefit Plan Obligations and Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2018	Dec. 30, 2018	Dec. 31, 2017
Change in plan assets:
Fair value of plan assets, beginning of period	$ 102,414
Fair value of plan assets, end of period	107,371
Pension Benefits
Change in projected benefit obligation:
Projected benefit obligation, beginning of period	157,619	$ 178,247
Interest cost	1,467	1,366
Actuarial losses (gains)	4,235	(6,829)
Benefits paid	(5,611)	(2,174)
Projected benefit obligation, end of period	157,710	170,610
Change in plan assets:
Fair value of plan assets, beginning of period	102,414	112,570
Actual return on plan assets	8,816	541
Contributions by employer	1,752	2,888
Benefits paid	(5,611)	(2,174)
Fair value of plan assets, end of period	107,371	113,825
Funded status:
Unfunded benefit obligation, end of period	(50,339)		$ (55,205)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(8,253)		(8,267)
Long-term liability	(42,086)		(46,938)
Recognized liability	(50,339)		(55,205)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	50,783	48,081	54,343	$ 54,235
Other Benefits
Change in projected benefit obligation:
Projected benefit obligation, beginning of period	1,462	1,603
Interest cost	13	12
Actuarial losses (gains)	32	(48)
Benefits paid	(37)	(37)
Projected benefit obligation, end of period	1,470	1,530
Change in plan assets:
Fair value of plan assets, beginning of period	0	0
Actual return on plan assets	0	0
Contributions by employer	37	37
Benefits paid	(37)	(37)
Fair value of plan assets, end of period	0	0
Funded status:
Unfunded benefit obligation, end of period	(1,470)		(1,462)
Amounts recognized in the Condensed Consolidated Balance Sheets at end of period:
Current liability	(148)		(149)
Long-term liability	(1,322)		(1,313)
Recognized liability	(1,470)		(1,462)
Amounts recognized in accumulated other comprehensive loss at end of period:
Net actuarial loss (gain)	$ (2)	$ (13)	$ (34)	$ 35