GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION (Details 4) - USD ($) $ / shares in Units, $ 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
Defined benefit pension plan expense (benefit)									$ (2,251)	$ 648	$ 1,870
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									440,220	414,688	410,869
Impairment of goodwill and intangible assets									15,780	0	0
Operating Income (Loss)									202,280	267,080	245,374
Interest Expense									(44,237)	(44,645)	(44,409)
Interest income									4,668	4,737	3,105
Other									(19,270)	1,292	16,384
Nonoperating Income (Expense)									(58,839)	(38,616)	(24,920)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									143,441	228,464	220,454
Current									44,794	66,390	65,748
Deferred									(1,659)	39,755	(23,685)
Income Tax Expense (Benefit)									43,135	106,145	42,063
Income (Loss) from Continuing Operations before Minority Interest and Income (Loss) from Equity Method Investments									100,306	122,319	178,391
Equity in earnings of nonconsolidated subsidiaries									0	0	0
Net earnings									100,306	122,319	178,391
Net Income (Loss) Attributable to Noncontrolling Interest									(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
Common stock, par value (in dollars per share)	$ 1				$ 1				$ 1	$ 1
Parent
Defined benefit pension plan expense (benefit)									$ 0	$ 0	0
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										192,182	184,493
Operating Income (Loss)									93,145	109,200	104,876
Interest Expense									(42,524)	(43,642)	(43,703)
Interest income									791	838	273
Other									(17,602)	5,681	1,480
Nonoperating Income (Expense)									(59,335)	(37,123)	(41,950)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									33,810	72,077	62,926
Current									6,310	29,407	24,539
Deferred									1,532	10,307	6,216
Income Tax Expense (Benefit)									7,842	39,714	30,755
Income (Loss) from Continuing Operations before Minority Interest and Income (Loss) from Equity Method Investments									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
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net earnings attributable to Valmont Industries, Inc.									94,351	116,240	173,232
Guarantor Subsidiaries [Member]
Defined benefit pension plan expense (benefit)									0	0	0
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										47,955	46,244
Operating Income (Loss)									71,788	62,110	58,588
Interest Expense									(14,815)	(13,866)	(10)
Interest income									82	42	112
Other									59	58	77
Nonoperating Income (Expense)									(14,674)	(13,766)	179
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									57,114	48,344	58,767
Current									14,948	17,928	20,270
Deferred									1,791	0	0
Income Tax Expense (Benefit)									16,739	17,928	20,270
Income (Loss) from Continuing Operations before Minority Interest and Income (Loss) from Equity Method Investments									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
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net earnings attributable to Valmont Industries, Inc.									77,679	52,562	104,625
Non-Guarantor Subsidiaries [Member]
Defined benefit pension plan expense (benefit)									(2,251)	648	1,870
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										174,551	180,132
Operating Income (Loss)									35,578	95,464	83,071
Interest Expense									(1,713)	(1,003)	(696)
Interest income									18,610	17,723	2,720
Other									(1,727)	(4,447)	14,827
Nonoperating Income (Expense)									15,170	12,273	16,851
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									50,748	107,737	99,922
Current									23,290	18,920	21,262
Deferred									(4,982)	29,448	(29,901)
Income Tax Expense (Benefit)									18,308	48,368	(8,639)
Income (Loss) from Continuing Operations before Minority Interest and Income (Loss) from Equity Method Investments									32,440	59,369	108,561
Equity in earnings of nonconsolidated subsidiaries									0	0	0
Net earnings									32,440	59,369	108,561
Net Income (Loss) Attributable to Noncontrolling Interest									(5,955)	(6,079)	(5,159)
Net earnings attributable to Valmont Industries, Inc.									26,485	53,290	103,402
Eliminations
Defined benefit pension plan expense (benefit)									0	0	0
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										0	0
Operating Income (Loss)									1,769	306	(1,161)
Interest Expense									14,815	13,866	0
Interest income									14,815	(13,866)	0
Other									0	0	0
Nonoperating Income (Expense)									0	0	0
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									1,769	306	(1,161)
Current									246	135	(323)
Deferred									0	0	0
Income Tax Expense (Benefit)									246	135	(323)
Income (Loss) from Continuing Operations before Minority Interest and Income (Loss) from Equity Method Investments									1,523	171	(838)
Equity in earnings of nonconsolidated subsidiaries									(105,687)	(106,023)	(207,189)
Net earnings									(104,164)	(105,852)	(208,027)
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net earnings attributable to Valmont Industries, Inc.									$ (104,164)	$ (105,852)	$ (208,027)