GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	$ 37,455	$ 40,480
Foreign currency translation adjustments:
Unrealized translation gain	2,266	6,804
Gain (loss) on hedging activities	2,314	(863)
Equity in other comprehensive income	0	0
Other comprehensive income	4,580	5,941
Comprehensive income	42,035	46,421
Comprehensive income attributable to noncontrolling interests	(1,109)	(4,747)
Comprehensive income attributable to Valmont Industries, Inc.	40,926	41,674
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	(30,474)	(25,741)
Foreign currency translation adjustments:
Unrealized translation gain	0	0
Gain (loss) on hedging activities	0	0
Equity in other comprehensive income	(2,131)	(3,256)
Other comprehensive income	(2,131)	(3,256)
Comprehensive income	(32,605)	(28,997)
Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(32,605)	(28,997)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	36,481	39,281
Foreign currency translation adjustments:
Unrealized translation gain	0	0
Gain (loss) on hedging activities	2,314	(863)
Equity in other comprehensive income	2,131	3,256
Other comprehensive income	4,445	2,393
Comprehensive income	40,926	41,674
Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income attributable to Valmont Industries, Inc.	40,926	41,674
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	23,561	10,989
Foreign currency translation adjustments:
Unrealized translation gain	5,629	(8,680)
Gain (loss) on hedging activities	0	0
Equity in other comprehensive income	0	0
Other comprehensive income	5,629	(8,680)
Comprehensive income	29,190	2,309
Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income attributable to Valmont Industries, Inc.	29,190	2,309
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	7,887	15,951
Foreign currency translation adjustments:
Unrealized translation gain	(3,363)	15,484
Gain (loss) on hedging activities	0	0
Equity in other comprehensive income	0	0
Other comprehensive income	(3,363)	15,484
Comprehensive income	4,524	31,435
Comprehensive income attributable to noncontrolling interests	(1,109)	(4,747)
Comprehensive income attributable to Valmont Industries, Inc.	$ 3,415	$ 26,688