GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION
Parent company's percentage ownership of Guarantors	100.00%
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	$ 692,139	$ 698,684
Cost of sales	527,010	529,444
Gross profit	165,129	169,240
Selling, general and administrative expenses	110,025	105,280
Operating income	55,104	63,960
Other income (expense):
Interest expense	(9,878)	(11,074)
Interest income	810	1,267
Other	3,846	(1,141)
Total other income (expenses)	(5,222)	(10,948)
Earnings before income taxes	49,882	53,012
Income tax expense (benefit):
Deferred income taxes	9,662	4,819
Total income tax expense (benefit)	12,427	12,532
Earnings before equity in earnings of nonconsolidated subsidiaries	37,455	40,480
Equity in earnings of nonconsolidated subsidiaries	0	0
Net earnings	37,455	40,480
Less: Earnings attributable to noncontrolling interests	(974)	(1,199)
Net earnings attributable to Valmont Industries, Inc.	36,481	39,281
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	(58,661)	(70,615)
Cost of sales	(59,036)	(72,327)
Gross profit	375	1,712
Selling, general and administrative expenses	0	0
Operating income	375	1,712
Other income (expense):
Interest expense	3,541	3,880
Interest income	(3,541)	(3,880)
Other		0
Total other income (expenses)	0	0
Earnings before income taxes	375	1,712
Income tax expense (benefit):
Deferred income taxes	0	0
Total income tax expense (benefit)	56	137
Earnings before equity in earnings of nonconsolidated subsidiaries	319	1,575
Equity in earnings of nonconsolidated subsidiaries	(30,793)	(27,316)
Net earnings	(30,474)	(25,741)
Less: Earnings attributable to noncontrolling interests	0	0
Net earnings attributable to Valmont Industries, Inc.	(30,474)	(25,741)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	299,002	315,992
Cost of sales	225,127	235,596
Gross profit	73,875	80,396
Selling, general and administrative expenses	57,846	46,531
Operating income	16,029	33,865
Other income (expense):
Interest expense	(9,583)	(10,881)
Interest income	111	176
Other	3,537	(106)
Total other income (expenses)	(5,935)	(10,811)
Earnings before income taxes	10,094	23,054
Income tax expense (benefit):
Deferred income taxes	5,320	5,591
Total income tax expense (benefit)	462	8,360
Earnings before equity in earnings of nonconsolidated subsidiaries	9,632	14,694
Equity in earnings of nonconsolidated subsidiaries	26,849	24,587
Net earnings	36,481	39,281
Less: Earnings attributable to noncontrolling interests	0	0
Net earnings attributable to Valmont Industries, Inc.	36,481	39,281
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	139,507	121,171
Cost of sales	103,312	94,459
Gross profit	36,195	26,712
Selling, general and administrative expenses	7,109	11,917
Operating income	29,086	14,795
Other income (expense):
Interest expense	(3,541)	(3,880)
Interest income	12	10
Other	10	12
Total other income (expenses)	(3,519)	(3,858)
Earnings before income taxes	25,567	10,937
Income tax expense (benefit):
Deferred income taxes	0	1,791
Total income tax expense (benefit)	5,950	2,677
Earnings before equity in earnings of nonconsolidated subsidiaries	19,617	8,260
Equity in earnings of nonconsolidated subsidiaries	3,944	2,729
Net earnings	23,561	10,989
Less: Earnings attributable to noncontrolling interests	0	0
Net earnings attributable to Valmont Industries, Inc.	23,561	10,989
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	312,291	332,136
Cost of sales	257,607	271,716
Gross profit	54,684	60,420
Selling, general and administrative expenses	45,070	46,832
Operating income	9,614	13,588
Other income (expense):
Interest expense	(295)	(193)
Interest income	4,228	4,961
Other	299	(1,047)
Total other income (expenses)	4,232	3,721
Earnings before income taxes	13,846	17,309
Income tax expense (benefit):
Deferred income taxes	4,342	(2,563)
Total income tax expense (benefit)	5,959	1,358
Earnings before equity in earnings of nonconsolidated subsidiaries	7,887	15,951
Equity in earnings of nonconsolidated subsidiaries	0	0
Net earnings	7,887	15,951
Less: Earnings attributable to noncontrolling interests	(974)	(1,199)
Net earnings attributable to Valmont Industries, Inc.	$ 6,913	$ 14,752