GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	$ 159,466	$ 100,306	$ 122,319
Foreign currency translation adjustments:
Unrealized translation gains (losses)	(2,506)	(65,436)	79,279
Realized loss on divestiture of grinding media business recorded in other expense	0	9,203	0
Gain (loss) on hedging activities	2,905	4,814	(1,621)
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan liability	(10,828)	29,885	(10,871)
Equity in other comprehensive income	0	0	0
Other comprehensive income (loss)	(10,429)	(21,534)	66,787
Comprehensive income (loss)	149,037	78,772	189,106
Comprehensive income attributable to noncontrolling interests	(5,505)	(8,584)	(5,529)
Comprehensive income (loss) attributable to Valmont Industries, Inc.	143,532	70,188	183,577
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	(112,439)	(104,164)	(105,852)
Foreign currency translation adjustments:
Unrealized translation gains (losses)	0	0	0
Realized loss on divestiture of grinding media business recorded in other expense	0	0
Gain (loss) on hedging activities	0	0	0
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan liability	0	0	0
Equity in other comprehensive income	13,142	28,977	(68,958)
Other comprehensive income (loss)	13,142	28,977	(68,958)
Comprehensive income (loss)	(99,297)	(75,187)	(174,810)
Comprehensive income attributable to noncontrolling interests	0	0	0
Comprehensive income (loss) attributable to Valmont Industries, Inc.	(99,297)	(75,187)	(174,810)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	153,769	94,351	116,240
Foreign currency translation adjustments:
Unrealized translation gains (losses)	0	0	0
Realized loss on divestiture of grinding media business recorded in other expense	0	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,905
Gain (loss) on hedging activities		4,814	(1,621)
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan liability	0	0	0
Equity in other comprehensive income	(13,142)	(28,977)	68,958
Other comprehensive income (loss)	(10,237)	(24,163)	67,337
Comprehensive income (loss)	143,532	70,188	183,577
Comprehensive income attributable to noncontrolling interests	0	0	0
Comprehensive income (loss) attributable to Valmont Industries, Inc.	143,532	70,188	183,577
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	75,581	77,679	52,562
Foreign currency translation adjustments:
Unrealized translation gains (losses)	(1,564)	(6,509)	138,795
Realized loss on divestiture of grinding media business recorded in other expense	0	0
Gain (loss) on hedging activities	0	0	0
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan liability	0	0	0
Equity in other comprehensive income	0	0	0
Other comprehensive income (loss)	(1,564)	(6,509)	138,795
Comprehensive income (loss)	74,017	71,170	191,357
Comprehensive income attributable to noncontrolling interests	0	0	0
Comprehensive income (loss) attributable to Valmont Industries, Inc.	74,017	71,170	191,357
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	42,555	32,440	59,369
Foreign currency translation adjustments:
Unrealized translation gains (losses)	(942)	(58,927)	(59,516)
Realized loss on divestiture of grinding media business recorded in other expense	0	9,203
Gain (loss) on hedging activities	0	0	0
Unrealized gain/(loss) on cash flow hedge:
Actuarial gain (loss) in defined benefit pension plan liability	(10,828)	29,885	(10,871)
Equity in other comprehensive income	0	0	0
Other comprehensive income (loss)	(11,770)	(19,839)	(70,387)
Comprehensive income (loss)	30,785	12,601	(11,018)
Comprehensive income attributable to noncontrolling interests	(5,505)	(8,584)	(5,529)
Comprehensive income (loss) attributable to Valmont Industries, Inc.	$ 25,280	$ 4,017	$ (16,547)