GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	$ 42,346	$ 34,680	$ 79,801	$ 75,160
Foreign currency translation adjustments:
Unrealized translation gain	1,049	(46,953)	3,315	(40,149)
Realized loss on divestiture of grinding media business recorded in earnings	0	9,203	0	9,203
Gain (loss) on hedging activities	(5,347)	2,607	(3,033)	1,744
Equity in other comprehensive income	0	0	0	0
Other comprehensive income	(4,298)	(35,143)	282	(29,202)
Comprehensive income	38,048	(463)	80,083	45,958
Comprehensive income attributable to noncontrolling interests	(983)	(1,114)	(2,092)	(5,861)
Comprehensive income attributable to Valmont Industries, Inc.	37,065	(1,577)	77,991	40,097
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	(21,286)	(52,879)	(51,760)	(78,620)
Foreign currency translation adjustments:
Unrealized translation gain	0	0	0	0
Realized loss on divestiture of grinding media business recorded in earnings		0		0
Gain (loss) on hedging activities	0	0	0	0
Equity in other comprehensive income	(1,015)	37,144	(3,146)	33,888
Other comprehensive income	(1,015)	37,144	(3,146)	33,888
Comprehensive income	(22,301)	(15,735)	(54,906)	(44,732)
Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(22,301)	(15,735)	(54,906)	(44,732)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	41,397	32,960	77,878	72,241
Foreign currency translation adjustments:
Unrealized translation gain	0	0	0	0
Realized loss on divestiture of grinding media business recorded in earnings		0		0
Gain (loss) on hedging activities	(5,347)	2,607	(3,033)	1,744
Equity in other comprehensive income	1,015	(37,144)	3,146	(33,888)
Other comprehensive income	(4,332)	(34,537)	113	(32,144)
Comprehensive income	37,065	(1,577)	77,991	40,097
Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	37,065	(1,577)	77,991	40,097
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	10,459	44,967	34,020	55,956
Foreign currency translation adjustments:
Unrealized translation gain	(9,850)	6,513	(4,221)	(2,167)
Realized loss on divestiture of grinding media business recorded in earnings		0		0
Gain (loss) on hedging activities	0	0	0	0
Equity in other comprehensive income	0	0	0	0
Other comprehensive income	(9,850)	6,513	(4,221)	(2,167)
Comprehensive income	609	51,480	29,799	53,789
Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	609	51,480	29,799	53,789
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	11,776	9,632	19,663	25,583
Foreign currency translation adjustments:
Unrealized translation gain	10,899	(53,466)	7,536	(37,982)
Realized loss on divestiture of grinding media business recorded in earnings		9,203		9,203
Gain (loss) on hedging activities	0	0	0	0
Equity in other comprehensive income	0	0	0	0
Other comprehensive income	10,899	(44,263)	7,536	(28,779)
Comprehensive income	22,675	(34,631)	27,199	(3,196)
Comprehensive income attributable to noncontrolling interests	(983)	(1,114)	(2,092)	(5,861)
Comprehensive income attributable to Valmont Industries, Inc.	$ 21,692	$ (35,745)	$ 25,107	$ (9,057)