GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	$ 34,680	$ 47,322	$ 75,160	$ 87,283
Foreign currency translation adjustments:
Unrealized translation gain (loss)	(46,953)	21,551	(40,149)	40,941
Realized loss on divestiture of grinding media business recorded in earnings	9,203	0	9,203	0
Gain (loss) on hedging activities:
Net investment hedges	2,396	(550)	1,607	(1,076)
Realized loss on net investment hedge for grinding media business recorded in earnings	1,215	0	1,215	0
Amortization cost included in interest expense	25	18	44	37
Loss (deferred) on interest rate hedges	(2,467)	0	(2,467)	0
Commodity hedges	1,438	0	1,345	0
Equity in other comprehensive income	0	0	0	0
Other comprehensive income (loss)	(35,143)	21,019	(29,202)	39,902
Comprehensive income	(463)	68,341	45,958	127,185
Comprehensive loss (income) attributable to noncontrolling interests	(1,114)	(2,223)	(5,861)	(1,982)
Comprehensive income attributable to Valmont Industries, Inc.	(1,577)	66,118	40,097	125,203
Consolidation, Eliminations [Member]
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	(52,879)	(34,569)	(78,620)	(62,555)
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:
Net investment hedges	0	0	0	0
Realized loss on net investment hedge for grinding media business recorded in earnings	0		0
Amortization cost included in interest expense	0	0	0	0
Loss (deferred) on interest rate hedges	0		0
Commodity hedges	0		0
Equity in other comprehensive income	37,144	(20,986)	33,888	(41,599)
Other comprehensive income (loss)	37,144	(20,986)	33,888	(41,599)
Comprehensive income	(15,735)	(55,555)	(44,732)	(104,154)
Comprehensive loss (income) attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(15,735)	(55,555)	(44,732)	(104,154)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	32,960	45,664	72,241	84,643
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:
Net investment hedges	2,396	(550)	1,607	(1,076)
Realized loss on net investment hedge for grinding media business recorded in earnings	1,215		1,215
Amortization cost included in interest expense	25	18	44	37
Loss (deferred) on interest rate hedges	(2,467)		(2,467)
Commodity hedges	1,438		1,345
Equity in other comprehensive income	(37,144)	20,986	(33,888)	41,599
Other comprehensive income (loss)	(34,537)	20,454	(32,144)	40,560
Comprehensive income	(1,577)	66,118	40,097	125,203
Comprehensive loss (income) attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	(1,577)	66,118	40,097	125,203
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	44,967	16,890	55,956	22,430
Foreign currency translation adjustments:
Unrealized translation gain (loss)	6,513	(1,359)	(2,167)	68,024
Realized loss on divestiture of grinding media business recorded in earnings	0		0
Gain (loss) on hedging activities:
Net investment hedges	0	0	0	0
Realized loss on net investment hedge for grinding media business recorded in earnings	0		0
Amortization cost included in interest expense	0	0	0	0
Loss (deferred) on interest rate hedges	0		0
Commodity hedges	0		0
Equity in other comprehensive income	0	0	0	0
Other comprehensive income (loss)	6,513	(1,359)	(2,167)	68,024
Comprehensive income	51,480	15,531	53,789	90,454
Comprehensive loss (income) attributable to noncontrolling interests	0	0	0	0
Comprehensive income attributable to Valmont Industries, Inc.	51,480	15,531	53,789	90,454
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net earnings	9,632	19,337	25,583	42,765
Foreign currency translation adjustments:
Unrealized translation gain (loss)	(53,466)	22,910	(37,982)	(27,083)
Realized loss on divestiture of grinding media business recorded in earnings	9,203		9,203
Gain (loss) on hedging activities:
Net investment hedges	0	0	0	0
Realized loss on net investment hedge for grinding media business recorded in earnings	0		0
Amortization cost included in interest expense	0	0	0	0
Loss (deferred) on interest rate hedges	0		0
Commodity hedges	0		0
Equity in other comprehensive income	0	0	0	0
Other comprehensive income (loss)	(44,263)	22,910	(28,779)	(27,083)
Comprehensive income	(34,631)	42,247	(3,196)	15,682
Comprehensive loss (income) attributable to noncontrolling interests	(1,114)	(2,223)	(5,861)	(1,982)
Comprehensive income attributable to Valmont Industries, Inc.	$ (35,745)	$ 40,024	$ (9,057)	$ 13,700