GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION (Details 2) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 30, 2019	Mar. 31, 2018	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings			$ 100,306	$ 122,319	$ 178,391
Foreign currency translation adjustments:
Unrealized translation gains (losses)			(65,436)	79,279	(58,315)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax			9,203		0
Gain (Loss) on Hedging Activity			4,814	(1,621)	4,300
Unrealized gain/(loss) on cash flow hedge:
Unrealized gain (loss) on net investment hedge	$ 5,291	$ (1,695)			4,226
Amortization cost included in interest expense			423	74	74
Realized loss on grinding media net investment hedge	1,215	0			0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ 1,021	$ 0			0
Derivative adjustment			4,814	(1,621)	4,300
Actuarial gain (loss) in defined benefit pension plan			29,885	(10,871)	(24,141)
Equity in other comprehensive income			0	0	0
Other comprehensive income (loss)			(21,534)	66,787	(78,156)
Comprehensive income (loss)			78,772	189,106	100,235
Comprehensive income attributable to noncontrolling interests			(8,584)	(5,529)	(6,144)
Comprehensive income (loss) attributable to Valmont Industries, Inc.			70,188	183,577	94,091
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings			(104,164)	(105,852)	(208,027)
Foreign currency translation adjustments:
Unrealized translation gains (losses)			0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax			0
Gain (Loss) on Hedging Activity			0	0	0
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan			0	0	0
Equity in other comprehensive income			28,977	(68,958)	83,252
Other comprehensive income (loss)			28,977	(68,958)	83,252
Comprehensive income (loss)			(75,187)	(174,810)	(124,775)
Comprehensive income attributable to noncontrolling interests			0	0	0
Comprehensive income (loss) attributable to Valmont Industries, Inc.			(75,187)	(174,810)	(124,775)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings			94,351	116,240	173,232
Foreign currency translation adjustments:
Unrealized translation gains (losses)			0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax			0
Gain (Loss) on Hedging Activity			4,814	(1,621)	4,300
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan			0	0	0
Equity in other comprehensive income			(28,977)	68,958	(83,252)
Other comprehensive income (loss)			(24,163)	67,337	(78,952)
Comprehensive income (loss)			70,188	183,577	94,280
Comprehensive income attributable to noncontrolling interests			0	0	0
Comprehensive income (loss) attributable to Valmont Industries, Inc.			70,188	183,577	94,280
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings			77,679	52,562	104,625
Foreign currency translation adjustments:
Unrealized translation gains (losses)			(6,509)	138,795	49
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax			0
Gain (Loss) on Hedging Activity			0	0	0
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan			0	0	0
Equity in other comprehensive income			0	0	0
Other comprehensive income (loss)			(6,509)	138,795	49
Comprehensive income (loss)			71,170	191,357	104,674
Comprehensive income attributable to noncontrolling interests			0	0	0
Comprehensive income (loss) attributable to Valmont Industries, Inc.			71,170	191,357	104,674
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings			32,440	59,369	108,561
Foreign currency translation adjustments:
Unrealized translation gains (losses)			(58,927)	(59,516)	(58,364)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax			9,203
Gain (Loss) on Hedging Activity			0	0	0
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan			29,885	(10,871)	(24,141)
Equity in other comprehensive income			0	0	0
Other comprehensive income (loss)			(19,839)	(70,387)	(82,505)
Comprehensive income (loss)			12,601	(11,018)	26,056
Comprehensive income attributable to noncontrolling interests			(8,584)	(5,529)	(6,144)
Comprehensive income (loss) attributable to Valmont Industries, Inc.			$ 4,017	$ (16,547)	$ 19,912