GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	$ 6,991	$ 36,666	$ 82,151	$ 123,949
Foreign currency translation adjustments:
Unrealized translation gain (loss)	(10,632)	19,530	(50,781)	60,471
Realized loss on divestiture of grinding media business recorded in earnings	0	0	9,203	0
Gain (loss) on hedging activities	(910)	(721)	834	(1,760)
Equity in other comprehensive income	0	0	0	0
Other comprehensive income (loss)	(11,542)	18,809	(40,744)	58,711
Comprehensive income (loss)	(4,551)	55,475	41,407	182,660
Comprehensive loss (income) attributable to noncontrolling interests	(2,389)	(2,570)	(8,250)	(4,552)
Comprehensive income attributable to Valmont Industries, Inc.	(6,940)	52,905	33,157	178,108
Consolidation, Eliminations [Member]
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	(13,592)	(38,160)	(92,212)	(100,715)
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	10,478	(18,418)	44,366	(60,017)
Other comprehensive income (loss)	10,478	(18,418)	44,366	(60,017)
Comprehensive income (loss)	(3,114)	(56,578)	(47,846)	(160,732)
Comprehensive loss (income) attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(3,114)	(56,578)	(47,846)	(160,732)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	4,448	35,208	76,689	119,851
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	(910)	(721)	834	(1,760)
Equity in other comprehensive income	(10,478)	18,418	(44,366)	60,017
Other comprehensive income (loss)	(11,388)	17,697	(43,532)	58,257
Comprehensive income (loss)	(6,940)	52,905	33,157	178,108
Comprehensive loss (income) attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(6,940)	52,905	33,157	178,108
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	14,792	15,354	70,748	37,784
Foreign currency translation adjustments:
Unrealized translation gain (loss)	4,289	(3,613)	2,122	64,411
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 (loss)	4,289	(3,613)	2,122	64,411
Comprehensive income (loss)	19,081	11,741	72,870	102,195
Comprehensive loss (income) attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	19,081	11,741	72,870	102,195
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	1,343	24,264	26,926	67,029
Foreign currency translation adjustments:
Unrealized translation gain (loss)	(14,921)	23,143	(52,903)	(3,940)
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 (loss)	(14,921)	23,143	(43,700)	(3,940)
Comprehensive income (loss)	(13,578)	47,407	(16,774)	63,089
Comprehensive loss (income) attributable to noncontrolling interests	(2,389)	(2,570)	(8,250)	(4,552)
Comprehensive income attributable to Valmont Industries, Inc.	$ (15,967)	$ 44,837	$ (25,024)	$ 58,537