GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
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	$ 697,363	$ 678,692	$ 682,405	$ 698,684	$ 714,978	$ 680,779	$ 712,737	$ 637,473	$ 2,757,144	$ 2,745,967	$ 2,521,676
Cost of sales									2,098,864	2,064,199	1,865,433
Gross profit	149,701	164,340	174,999	169,240	170,289	163,594	183,280	164,605	658,280	681,768	656,243
Selling, General And Administrative Expenses, And Goodwill And Intangible Assets Impairment									456,000
Impairment of goodwill and intangible assets									15,780	0	0
Operating income									202,280	267,080	245,374
Other income (expense):
Interest expense									(44,237)	(44,645)	(44,409)
Interest income									(4,668)	(4,737)	(3,105)
Costs associated with refinancing of debt									(14,820)	0	0
Other									(19,270)	1,292	16,384
Total other income (expenses)									(58,839)	(38,616)	(24,920)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									143,441	228,464	220,454
Income tax expense (benefit):
Current									44,794	66,390	65,748
Deferred income taxes									(1,659)	39,755	(23,685)
Total income tax expense (benefit)									43,135	106,145	42,063
Earnings before equity in earnings of nonconsolidated subsidiaries									100,306	122,319	178,391
Equity in earnings of nonconsolidated subsidiaries									0	0	0
Net earnings									100,306	122,319	178,391
Less: Earnings attributable to noncontrolling interests									(5,955)	(6,079)	(5,159)
Net earnings attributable to Valmont Industries, Inc.	$ 17,662	$ 4,448	$ 32,960	$ 39,281	$ (3,611)	$ 35,208	$ 45,664	$ 38,979	94,351	116,240	173,232
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									(260,679)	(251,876)	(191,877)
Cost of sales									(262,448)	(252,182)	(190,716)
Gross profit									1,769	306	(1,161)
Selling, General And Administrative Expenses, And Goodwill And Intangible Assets Impairment									0
Operating income									1,769	306	(1,161)
Other income (expense):
Interest expense									14,815	13,866	0
Interest income									(14,815)	13,866	0
Other									0	0	0
Total other income (expenses)									0	0	0
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									1,769	306	(1,161)
Income tax expense (benefit):
Current									246	135	(323)
Deferred income taxes									0	0	0
Total income tax expense (benefit)									246	135	(323)
Earnings before equity in earnings of nonconsolidated subsidiaries									1,523	171	(838)
Equity in earnings of nonconsolidated subsidiaries									(105,687)	(106,023)	(207,189)
Net earnings									(104,164)	(105,852)	(208,027)
Less: Earnings attributable to noncontrolling interests									0	0	0
Net earnings attributable to Valmont Industries, Inc.									(104,164)	(105,852)	(208,027)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									1,192,134	1,200,181	1,126,985
Cost of sales									906,646	898,799	837,616
Gross profit									285,488	301,382	289,369
Selling, General And Administrative Expenses, And Goodwill And Intangible Assets Impairment									192,343
Operating income									93,145	109,200	104,876
Other income (expense):
Interest expense									(42,524)	(43,642)	(43,703)
Interest income									(791)	(838)	(273)
Other									(17,602)	5,681	1,480
Total other income (expenses)									(59,335)	(37,123)	(41,950)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									33,810	72,077	62,926
Income tax expense (benefit):
Current									6,310	29,407	24,539
Deferred income taxes									1,532	10,307	6,216
Total income tax expense (benefit)									7,842	39,714	30,755
Earnings before equity in earnings of nonconsolidated subsidiaries									25,968	32,363	32,171
Equity in earnings of nonconsolidated subsidiaries									68,383	83,877	141,061
Net earnings									94,351	116,240	173,232
Less: Earnings attributable to noncontrolling interests									0	0	0
Net earnings attributable to Valmont Industries, Inc.									94,351	116,240	173,232
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									522,366	485,448	390,756
Cost of sales									399,451	375,383	285,924
Gross profit									122,915	110,065	104,832
Selling, General And Administrative Expenses, And Goodwill And Intangible Assets Impairment									51,127
Operating income									71,788	62,110	58,588
Other income (expense):
Interest expense									(14,815)	(13,866)	(10)
Interest income									(82)	(42)	(112)
Other									59	58	77
Total other income (expenses)									(14,674)	(13,766)	179
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									57,114	48,344	58,767
Income tax expense (benefit):
Current									14,948	17,928	20,270
Deferred income taxes									1,791	0	0
Total income tax expense (benefit)									16,739	17,928	20,270
Earnings before equity in earnings of nonconsolidated subsidiaries									40,375	30,416	38,497
Equity in earnings of nonconsolidated subsidiaries									37,304	22,146	66,128
Net earnings									77,679	52,562	104,625
Less: Earnings attributable to noncontrolling interests									0	0	0
Net earnings attributable to Valmont Industries, Inc.									77,679	52,562	104,625
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales									1,303,323	1,312,214	1,195,812
Cost of sales									1,055,215	1,042,199	932,609
Gross profit									248,108	270,015	263,203
Selling, General And Administrative Expenses, And Goodwill And Intangible Assets Impairment									212,530
Operating income									35,578	95,464	83,071
Other income (expense):
Interest expense									(1,713)	(1,003)	(696)
Interest income									(18,610)	(17,723)	(2,720)
Other									(1,727)	(4,447)	14,827
Total other income (expenses)									15,170	12,273	16,851
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									50,748	107,737	99,922
Income tax expense (benefit):
Current									23,290	18,920	21,262
Deferred income taxes									(4,982)	29,448	(29,901)
Total income tax expense (benefit)									18,308	48,368	(8,639)
Earnings before equity in earnings of nonconsolidated subsidiaries									32,440	59,369	108,561
Equity in earnings of nonconsolidated subsidiaries									0	0	0
Net earnings									32,440	59,369	108,561
Less: Earnings attributable to noncontrolling interests									(5,955)	(6,079)	(5,159)
Net earnings attributable to Valmont Industries, Inc.									$ 26,485	$ 53,290	$ 103,402