GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Earnings (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 29, 2019 USD ($) tranche	Jun. 30, 2018 USD ($)	Jun. 29, 2019 USD ($) tranche	Jun. 30, 2018 USD ($)
GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION
Number of tranches of senior unsecured notes | tranche	2		2
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	$ 700,871	$ 682,405	$ 1,393,010	$ 1,381,089
Cost of sales	520,457	507,406	1,047,467	1,036,850
Gross profit	180,414	174,999	345,543	344,239
Selling, general and administrative expenses	116,702	111,329	226,727	216,609
Operating income	63,712	63,670	118,816	127,630
Other income (expense):
Interest expense	(10,117)	(11,791)	(19,995)	(22,865)
Interest income	1,036	1,446	1,846	2,713
Loss from divestiture of grinding media business	0	(6,084)	0	(6,084)
Other	1,676	1,844	5,522	703
Total other income (expenses)	(7,405)	(14,585)	(12,627)	(25,533)
Earnings before income taxes	56,307	49,085	106,189	102,097
Income tax expense (benefit):
Deferred income taxes	(3,952)	(2,319)	5,710	2,500
Total income tax expense (benefit)	13,961	14,405	26,388	26,937
Earnings before equity in earnings of nonconsolidated subsidiaries	42,346	34,680	79,801	75,160
Equity in earnings of nonconsolidated subsidiaries	0	0	0	0
Net earnings	42,346	34,680	79,801	75,160
Less: Earnings attributable to noncontrolling interests	(949)	(1,720)	(1,923)	(2,919)
Net earnings attributable to Valmont Industries, Inc.	41,397	32,960	77,878	72,241
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	(67,770)	(64,573)	(126,431)	(135,188)
Cost of sales	(67,222)	(64,105)	(126,258)	(136,432)
Gross profit	(548)	(468)	(173)	1,244
Selling, general and administrative expenses	0	0	0	0
Operating income	(548)	(468)	(173)	1,244
Other income (expense):
Interest expense	2,499	3,749	6,040	7,629
Interest income	(2,499)	(3,749)	(6,040)	(7,629)
Loss from divestiture of grinding media business		0		0
Other	0	0		0
Total other income (expenses)	0	0	0	0
Earnings before income taxes	(548)	(468)	(173)	1,244
Income tax expense (benefit):
Deferred income taxes			0	0
Total income tax expense (benefit)	(47)	(49)	9	88
Earnings before equity in earnings of nonconsolidated subsidiaries	(501)	(419)	(182)	1,156
Equity in earnings of nonconsolidated subsidiaries	(20,785)	(52,460)	(51,578)	(79,776)
Net earnings	(21,286)	(52,879)	(51,760)	(78,620)
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	(21,286)	(52,879)	(51,760)	(78,620)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	313,973	297,916	612,975	613,908
Cost of sales	226,017	220,677	451,144	456,273
Gross profit	87,956	77,239	161,831	157,635
Selling, general and administrative expenses	49,788	50,259	107,634	96,790
Operating income	38,168	26,980	54,197	60,845
Other income (expense):
Interest expense	(9,584)	(11,396)	(19,167)	(22,277)
Interest income	342	305	453	481
Loss from divestiture of grinding media business		(2,518)		(2,518)
Other	1,878	616	5,415	510
Total other income (expenses)	(7,364)	(12,993)	(13,299)	(23,804)
Earnings before income taxes	30,804	13,987	40,898	37,041
Income tax expense (benefit):
Deferred income taxes			1,317	3,343
Total income tax expense (benefit)	7,310	2,318	7,772	10,678
Earnings before equity in earnings of nonconsolidated subsidiaries	23,494	11,669	33,126	26,363
Equity in earnings of nonconsolidated subsidiaries	17,903	21,291	44,752	45,878
Net earnings	41,397	32,960	77,878	72,241
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	41,397	32,960	77,878	72,241
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	138,151	133,563	277,658	254,734
Cost of sales	107,331	98,649	210,643	193,108
Gross profit	30,820	34,914	67,015	61,626
Selling, general and administrative expenses	18,867	12,535	25,976	24,452
Operating income	11,953	22,379	41,039	37,174
Other income (expense):
Interest expense	(2,498)	(3,749)	(6,039)	(7,629)
Interest income	18	5	30	15
Loss from divestiture of grinding media business		0		0
Other	11	14	21	26
Total other income (expenses)	(2,469)	(3,730)	(5,988)	(7,588)
Earnings before income taxes	9,484	18,649	35,051	29,586
Income tax expense (benefit):
Deferred income taxes			0	1,791
Total income tax expense (benefit)	1,907	4,851	7,857	7,528
Earnings before equity in earnings of nonconsolidated subsidiaries	7,577	13,798	27,194	22,058
Equity in earnings of nonconsolidated subsidiaries	2,882	31,169	6,826	33,898
Net earnings	10,459	44,967	34,020	55,956
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	10,459	44,967	34,020	55,956
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	316,517	315,499	628,808	647,635
Cost of sales	254,331	252,185	511,938	523,901
Gross profit	62,186	63,314	116,870	123,734
Selling, general and administrative expenses	48,047	48,535	93,117	95,367
Operating income	14,139	14,779	23,753	28,367
Other income (expense):
Interest expense	(534)	(395)	(829)	(588)
Interest income	3,175	4,885	7,403	9,846
Loss from divestiture of grinding media business		(3,566)		(3,566)
Other	(213)	1,214	86	167
Total other income (expenses)	2,428	2,138	6,660	5,859
Earnings before income taxes	16,567	16,917	30,413	34,226
Income tax expense (benefit):
Deferred income taxes			4,393	(2,634)
Total income tax expense (benefit)	4,791	7,285	10,750	8,643
Earnings before equity in earnings of nonconsolidated subsidiaries	11,776	9,632	19,663	25,583
Equity in earnings of nonconsolidated subsidiaries	0	0	0	0
Net earnings	11,776	9,632	19,663	25,583
Less: Earnings attributable to noncontrolling interests	(949)	(1,720)	(1,923)	(2,919)
Net earnings attributable to Valmont Industries, Inc.	$ 10,827	$ 7,912	$ 17,740	$ 22,664