GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION
Parent company's percentage ownership of Guarantors	100.00%								100.00%
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	$ 714,978	$ 680,779	$ 712,737	$ 637,473	$ 674,575	$ 610,247	$ 640,249	$ 596,605	$ 2,745,967	$ 2,521,676	$ 2,618,924
Cost of sales									2,064,199	1,865,433	1,997,891
Gross profit	170,289	163,594	183,280	164,605	165,135	155,023	175,117	160,968	681,768	656,243	621,033
Selling, general and administrative expenses									415,336	412,739	447,368
Impairment of goodwill and intangible assets									0	0	41,970
Operating income									266,432	243,504	131,695
Other income (expense):
Interest expense									(44,645)	(44,409)	(44,621)
Interest income									4,737	3,105	3,296
Other									1,940	18,254	2,637
Total other income (expenses)									(37,968)	(23,050)	(38,688)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									228,464	220,454	93,007
Income tax expense (benefit):
Current									66,390	65,748	42,569
Deferred income taxes									39,755	(23,685)	4,858
Total income tax expense (benefit)									106,145	42,063	47,427
Earnings before equity in earnings of nonconsolidated subsidiaries									122,319	178,391	45,580
Equity in earnings of nonconsolidated subsidiaries									0	0	(247)
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax									(12,568)	13,652	0
Net earnings									122,319	178,391	45,333
Less: Earnings attributable to noncontrolling interests									(6,079)	(5,159)	(5,216)
Net earnings attributable to Valmont Industries, Inc.	$ (3,611)	$ 35,208	$ 45,664	$ 38,979	$ 70,064	$ 28,173	$ 42,026	$ 32,969	116,240	173,232	40,117
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									(251,876)	(191,877)	(213,287)
Cost of sales									(252,182)	(190,716)	(212,927)
Gross profit									306	(1,161)	(360)
Selling, general and administrative expenses									0	0	0
Impairment of goodwill and intangible assets										0	0
Operating income									306	(1,161)	(360)
Other income (expense):
Interest expense									(13,866)	0	0
Interest income									(13,866)	0	0
Other									0	0	0
Total other income (expenses)									0	0	0
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									306	(1,161)	(360)
Income tax expense (benefit):
Current									135	(323)	(1)
Deferred income taxes									0	0	0
Total income tax expense (benefit)									135	(323)	(1)
Earnings before equity in earnings of nonconsolidated subsidiaries									171	(838)	(359)
Equity in earnings of nonconsolidated subsidiaries									(106,023)	(207,189)	27,576
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax										0
Net earnings									(105,852)	(208,027)	27,217
Less: Earnings attributable to noncontrolling interests									0	0	0
Net earnings attributable to Valmont Industries, Inc.									(105,852)	(208,027)	27,217
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									1,200,181	1,126,985	1,169,674
Cost of sales									898,799	837,616	890,242
Gross profit									301,382	289,369	279,432
Selling, general and administrative expenses									192,182	184,493	194,335
Impairment of goodwill and intangible assets										0	0
Operating income									109,200	104,876	85,097
Other income (expense):
Interest expense									(43,642)	(43,703)	(43,552)
Interest income									838	273	9
Other									5,681	1,480	(2,374)
Total other income (expenses)									(37,123)	(41,950)	(45,917)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									72,077	62,926	39,180
Income tax expense (benefit):
Current									29,407	24,539	863
Deferred income taxes									10,307	6,216	10,042
Total income tax expense (benefit)									39,714	30,755	10,905
Earnings before equity in earnings of nonconsolidated subsidiaries									32,363	32,171	28,275
Equity in earnings of nonconsolidated subsidiaries									83,877	141,061	11,842
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax										0
Net earnings									116,240	173,232	40,117
Less: Earnings attributable to noncontrolling interests									0	0	0
Net earnings attributable to Valmont Industries, Inc.									116,240	173,232	40,117
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									485,448	390,756	423,928
Cost of sales									375,383	285,924	332,847
Gross profit									110,065	104,832	91,081
Selling, general and administrative expenses									47,955	46,244	45,549
Impairment of goodwill and intangible assets										0	0
Operating income									62,110	58,588	45,532
Other income (expense):
Interest expense									(13,866)	(10)	0
Interest income									42	112	103
Other									58	77	60
Total other income (expenses)									(13,766)	179	163
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									48,344	58,767	45,695
Income tax expense (benefit):
Current									17,928	20,270	23,261
Deferred income taxes									0	0	(6,224)
Total income tax expense (benefit)									17,928	20,270	17,037
Earnings before equity in earnings of nonconsolidated subsidiaries									30,416	38,497	28,658
Equity in earnings of nonconsolidated subsidiaries									22,146	66,128	(39,418)
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax										0
Net earnings									52,562	104,625	(10,760)
Less: Earnings attributable to noncontrolling interests									0	0	0
Net earnings attributable to Valmont Industries, Inc.									52,562	104,625	(10,760)
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									1,312,214	1,195,812	1,238,609
Cost of sales									1,042,199	932,609	987,729
Gross profit									270,015	263,203	250,880
Selling, general and administrative expenses									175,199	182,002	207,484
Impairment of goodwill and intangible assets										0	41,970
Operating income									94,816	81,201	1,426
Other income (expense):
Interest expense									(1,003)	(696)	(1,069)
Interest income									17,723	2,720	3,184
Other									(3,799)	16,697	4,951
Total other income (expenses)									12,921	18,721	7,066
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									107,737	99,922	8,492
Income tax expense (benefit):
Current									18,920	21,262	18,446
Deferred income taxes									29,448	(29,901)	1,040
Total income tax expense (benefit)									48,368	(8,639)	19,486
Earnings before equity in earnings of nonconsolidated subsidiaries									59,369	108,561	(10,994)
Equity in earnings of nonconsolidated subsidiaries									0	0	(247)
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax										13,652
Net earnings									59,369	108,561	(11,241)
Less: Earnings attributable to noncontrolling interests									(6,079)	(5,159)	(5,216)
Net earnings attributable to Valmont Industries, Inc.									$ 53,290	$ 103,402	$ (16,457)