GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	$ 42,263	$ 6,991	$ 122,064	$ 82,151
Foreign currency translation adjustments:
Unrealized translation gain (loss)	(23,781)	(10,632)	(20,466)	(50,781)
Realized loss on divestiture of grinding media business recorded in earnings	0	0	0	9,203
Gain (loss) on hedging activities	9,315	(910)	6,282	834
Equity in other comprehensive income	0	0	0	0
Other comprehensive income	(14,466)	(11,542)	(14,184)	(40,744)
Comprehensive income	27,797	(4,551)	107,880	41,407
Comprehensive income attributable to noncontrolling interests	(1,297)	(2,389)	(3,390)	(8,250)
Comprehensive income attributable to Valmont Industries, Inc.	26,500	(6,940)	104,490	33,157
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	(41,396)	(13,592)	(93,156)	(92,212)
Foreign currency translation adjustments:
Unrealized translation gain (loss)	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	22,959	10,478	19,814	44,366
Other comprehensive income	22,959	10,478	19,814	44,366
Comprehensive income	(18,437)	(3,114)	(73,342)	(47,846)
Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(18,437)	(3,114)	(73,342)	(47,846)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	40,144	4,448	118,022	76,689
Foreign currency translation adjustments:
Unrealized translation gain (loss)	0	0	0	0
Realized loss on divestiture of grinding media business recorded in earnings		0		0
Gain (loss) on hedging activities	9,315	(910)	6,282	834
Equity in other comprehensive income	(22,959)	(10,478)	(19,814)	(44,366)
Other comprehensive income	(13,644)	(11,388)	(13,532)	(43,532)
Comprehensive income	26,500	(6,940)	104,490	33,157
Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	26,500	(6,940)	104,490	33,157
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	27,154	14,792	61,174	70,748
Foreign currency translation adjustments:
Unrealized translation gain (loss)	4,512	4,289	291	2,122
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	4,512	4,289	291	2,122
Comprehensive income	31,666	19,081	61,465	72,870
Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	31,666	19,081	61,465	72,870
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	16,361	1,343	36,024	26,926
Foreign currency translation adjustments:
Unrealized translation gain (loss)	(28,293)	(14,921)	(20,757)	(52,903)
Realized loss on divestiture of grinding media business recorded in earnings		0		9,203
Gain (loss) on hedging activities	0	0	0	0
Equity in other comprehensive income	0	0	0	0
Other comprehensive income	(28,293)	(14,921)	(20,757)	(43,700)
Comprehensive income	(11,932)	(13,578)	15,267	(16,774)
Comprehensive income attributable to noncontrolling interests	(1,297)	(2,389)	(3,390)	(8,250)
Comprehensive income attributable to Valmont Industries, Inc.	$ (13,229)	$ (15,967)	$ 11,877	$ (25,024)