GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
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	$ 682,405	$ 712,737	$ 1,381,089	$ 1,350,210
Cost of sales	507,406	529,457	1,036,850	1,002,325
Gross profit	174,999	183,280	344,239	347,885
Selling, general and administrative expenses	111,329	104,830	216,609	204,779
Operating income	63,670	78,450	127,630	143,106
Other income (expense):
Interest expense	(11,791)	(10,818)	(22,865)	(22,122)
Interest income	1,446	967	2,713	1,894
Loss from divestiture of grinding media business	(6,084)	0	(6,084)	0
Other	1,844	(192)	703	853
Total other income (expenses)	(14,585)	(10,043)	(25,533)	(19,375)
Earnings before income taxes	49,085	68,407	102,097	123,731
Income tax expense (benefit):
Current	16,724	27,803	24,437	29,101
Deferred income taxes	(2,319)	(6,718)	2,500	7,347
Total income tax expense (benefit)	14,405	21,085	26,937	36,448
Earnings before equity in earnings of nonconsolidated subsidiaries	34,680	47,322	75,160	87,283
Equity in earnings of nonconsolidated subsidiaries	0	0	0	0
Net earnings	34,680	47,322	75,160	87,283
Less: Earnings attributable to noncontrolling interests	(1,720)	(1,658)	(2,919)	(2,640)
Net earnings attributable to Valmont Industries, Inc.	32,960	45,664	72,241	84,643
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	(64,573)	(53,823)	(135,188)	(122,136)
Cost of sales	(64,105)	(54,610)	(136,432)	(122,207)
Gross profit	(468)	787	1,244	71
Selling, general and administrative expenses	0	0	0	0
Operating income	(468)	787	1,244	71
Other income (expense):
Interest expense	3,749	3,785	7,629	6,051
Interest income	(3,749)	(3,785)	(7,629)	(6,051)
Loss from divestiture of grinding media business	0		0
Other	0	0	0	0
Total other income (expenses)	0	0	0	0
Earnings before income taxes	(468)	787	1,244	71
Income tax expense (benefit):
Current	(49)	233	88	(11)
Deferred income taxes	0	0	0	0
Total income tax expense (benefit)	(49)	233	88	(11)
Earnings before equity in earnings of nonconsolidated subsidiaries	(419)	554	1,156	82
Equity in earnings of nonconsolidated subsidiaries	(52,460)	(35,123)	(79,776)	(62,637)
Net earnings	(52,879)	(34,569)	(78,620)	(62,555)
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	(52,879)	(34,569)	(78,620)	(62,555)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	297,916	316,185	613,908	609,450
Cost of sales	220,677	233,535	456,273	450,021
Gross profit	77,239	82,650	157,635	159,429
Selling, general and administrative expenses	50,259	46,922	96,790	97,139
Operating income	26,980	35,728	60,845	62,290
Other income (expense):
Interest expense	(11,396)	(10,646)	(22,277)	(21,788)
Interest income	305	144	481	295
Loss from divestiture of grinding media business	(2,518)		(2,518)
Other	616	1,167	510	2,521
Total other income (expenses)	(12,993)	(9,335)	(23,804)	(18,972)
Earnings before income taxes	13,987	26,393	37,041	43,318
Income tax expense (benefit):
Current	4,566	15,344	7,335	10,457
Deferred income taxes	(2,248)	(5,788)	3,343	5,539
Total income tax expense (benefit)	2,318	9,556	10,678	15,996
Earnings before equity in earnings of nonconsolidated subsidiaries	11,669	16,837	26,363	27,322
Equity in earnings of nonconsolidated subsidiaries	21,291	28,827	45,878	57,321
Net earnings	32,960	45,664	72,241	84,643
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	32,960	45,664	72,241	84,643
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	133,563	122,359	254,734	239,584
Cost of sales	98,649	91,374	193,108	182,863
Gross profit	34,914	30,985	61,626	56,721
Selling, general and administrative expenses	12,535	11,849	24,452	23,509
Operating income	22,379	19,136	37,174	33,212
Other income (expense):
Interest expense	(3,749)	(3,785)	(7,629)	(6,051)
Interest income	5	10	15	24
Loss from divestiture of grinding media business	0		0
Other	14	15	26	31
Total other income (expenses)	(3,730)	(3,760)	(7,588)	(5,996)
Earnings before income taxes	18,649	15,376	29,586	27,216
Income tax expense (benefit):
Current	4,851	4,782	5,737	10,102
Deferred income taxes	0	0	1,791	0
Total income tax expense (benefit)	4,851	4,782	7,528	10,102
Earnings before equity in earnings of nonconsolidated subsidiaries	13,798	10,594	22,058	17,114
Equity in earnings of nonconsolidated subsidiaries	31,169	6,296	33,898	5,316
Net earnings	44,967	16,890	55,956	22,430
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	44,967	16,890	55,956	22,430
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	315,499	328,016	647,635	623,312
Cost of sales	252,185	259,158	523,901	491,648
Gross profit	63,314	68,858	123,734	131,664
Selling, general and administrative expenses	48,535	46,059	95,367	84,131
Operating income	14,779	22,799	28,367	47,533
Other income (expense):
Interest expense	(395)	(172)	(588)	(334)
Interest income	4,885	4,598	9,846	7,626
Loss from divestiture of grinding media business	(3,566)		(3,566)
Other	1,214	(1,374)	167	(1,699)
Total other income (expenses)	2,138	3,052	5,859	5,593
Earnings before income taxes	16,917	25,851	34,226	53,126
Income tax expense (benefit):
Current	7,356	7,444	11,277	8,553
Deferred income taxes	(71)	(930)	(2,634)	1,808
Total income tax expense (benefit)	7,285	6,514	8,643	10,361
Earnings before equity in earnings of nonconsolidated subsidiaries	9,632	19,337	25,583	42,765
Equity in earnings of nonconsolidated subsidiaries	0	0	0	0
Net earnings	9,632	19,337	25,583	42,765
Less: Earnings attributable to noncontrolling interests	(1,720)	(1,658)	(2,919)	(2,640)
Net earnings attributable to Valmont Industries, Inc.	$ 7,912	$ 17,679	$ 22,664	$ 40,125