GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
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	$ 698,684	$ 637,473
Cost of sales	529,444	472,868
Gross profit	169,240	164,605
Selling, general and administrative expenses	105,280	99,949
Operating income	63,960	64,656
Other income (expense):
Interest expense	(11,074)	(11,304)
Interest income	1,267	927
Other	(1,141)	1,045
Total other income (expenses)	(10,948)	(9,332)
Earnings before income taxes	53,012	55,324
Income tax expense:
Current	7,713	1,298
Deferred income taxes	4,819	14,065
Total income tax expense (benefit)	12,532	15,363
Earnings before equity in earnings of nonconsolidated subsidiaries	40,480	39,961
Equity in earnings of nonconsolidated subsidiaries	0	0
Net earnings	40,480	39,961
Less: Earnings attributable to noncontrolling interests	(1,199)	(982)
Net earnings attributable to Valmont Industries, Inc.	39,281	38,979
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	(70,615)	(68,313)
Cost of sales	(72,327)	(67,597)
Gross profit	1,712	(716)
Selling, general and administrative expenses	0	0
Operating income	1,712	(716)
Other income (expense):
Interest expense	3,880	2,266
Interest income	(3,880)	(2,266)
Other	0	0
Total other income (expenses)	0	0
Earnings before income taxes	1,712	(716)
Income tax expense:
Current	137	(244)
Deferred income taxes	0	0
Total income tax expense (benefit)	137	(244)
Earnings before equity in earnings of nonconsolidated subsidiaries	1,575	(472)
Equity in earnings of nonconsolidated subsidiaries	(27,316)	(27,514)
Net earnings	(25,741)	(27,986)
Less: Earnings attributable to noncontrolling interests	0	0
Net earnings attributable to Valmont Industries, Inc.	(25,741)	(27,986)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	315,992	293,265
Cost of sales	235,596	216,486
Gross profit	80,396	76,779
Selling, general and administrative expenses	46,531	50,217
Operating income	33,865	26,562
Other income (expense):
Interest expense	(10,881)	(11,142)
Interest income	176	151
Other	(106)	1,354
Total other income (expenses)	(10,811)	(9,637)
Earnings before income taxes	23,054	16,925
Income tax expense:
Current	2,769	(4,887)
Deferred income taxes	5,591	11,327
Total income tax expense (benefit)	8,360	6,440
Earnings before equity in earnings of nonconsolidated subsidiaries	14,694	10,485
Equity in earnings of nonconsolidated subsidiaries	24,587	28,494
Net earnings	39,281	38,979
Less: Earnings attributable to noncontrolling interests	0	0
Net earnings attributable to Valmont Industries, Inc.	39,281	38,979
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	121,171	117,225
Cost of sales	94,459	91,489
Gross profit	26,712	25,736
Selling, general and administrative expenses	11,917	11,660
Operating income	14,795	14,076
Other income (expense):
Interest expense	(3,880)	(2,266)
Interest income	10	14
Other	12	16
Total other income (expenses)	(3,858)	(2,236)
Earnings before income taxes	10,937	11,840
Income tax expense:
Current	886	5,320
Deferred income taxes	1,791	0
Total income tax expense (benefit)	2,677	5,320
Earnings before equity in earnings of nonconsolidated subsidiaries	8,260	6,520
Equity in earnings of nonconsolidated subsidiaries	2,729	(980)
Net earnings	10,989	5,540
Less: Earnings attributable to noncontrolling interests	0	0
Net earnings attributable to Valmont Industries, Inc.	10,989	5,540
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	332,136	295,296
Cost of sales	271,716	232,490
Gross profit	60,420	62,806
Selling, general and administrative expenses	46,832	38,072
Operating income	13,588	24,734
Other income (expense):
Interest expense	(193)	(162)
Interest income	4,961	3,028
Other	(1,047)	(325)
Total other income (expenses)	3,721	2,541
Earnings before income taxes	17,309	27,275
Income tax expense:
Current	3,921	1,109
Deferred income taxes	(2,563)	2,738
Total income tax expense (benefit)	1,358	3,847
Earnings before equity in earnings of nonconsolidated subsidiaries	15,951	23,428
Equity in earnings of nonconsolidated subsidiaries	0	0
Net earnings	15,951	23,428
Less: Earnings attributable to noncontrolling interests	(1,199)	(982)
Net earnings attributable to Valmont Industries, Inc.	$ 14,752	$ 22,446