GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Earnings (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
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	$ 680,779	$ 610,247	$ 2,030,989	$ 1,847,101
Cost of sales	517,185	455,224	1,519,510	1,355,992
Gross profit	163,594	155,023	511,479	491,109
Selling, general and administrative expenses	103,671	101,783	308,764	303,698
Operating income	59,923	53,240	202,715	187,411
Other income (expense):
Interest expense	(11,190)	(11,100)	(33,312)	(33,276)
Interest income	1,311	771	3,205	2,289
Other	517	878	1,684	452
Total other income (expenses)	(9,362)	(9,451)	(28,423)	(30,535)
Earnings before income taxes	50,561	43,789	174,292	156,876
Income tax expense:
Current	21,163	18,017	50,264	51,276
Deferred income taxes	(7,268)	(3,749)	79	(1,534)
Total income tax expense (benefit)	13,895	14,268	50,343	49,742
Earnings before equity in earnings of nonconsolidated subsidiaries	36,666	29,521	123,949	107,134
Equity in earnings of nonconsolidated subsidiaries	0	0	0	0
Net earnings	36,666	29,521	123,949	107,134
Less: Earnings attributable to noncontrolling interests	(1,458)	(1,348)	(4,098)	(3,966)
Net earnings attributable to Valmont Industries, Inc.	35,208	28,173	119,851	103,168
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	(60,820)	(41,634)	(182,956)	(141,699)
Cost of sales	(60,570)	(41,695)	(182,777)	(140,200)
Gross profit	(250)	61	(179)	(1,499)
Selling, general and administrative expenses	0	0	0	0
Operating income	(250)	61	(179)	(1,499)
Other income (expense):
Interest expense	3,989	0	10,040	0
Interest income	(3,989)	0	(10,040)	0
Other	0	0	0	0
Total other income (expenses)	0	0	0	0
Earnings before income taxes	(250)	61	(179)	(1,499)
Income tax expense:
Current	(8)	48	(19)	(481)
Deferred income taxes	0	0	0	0
Total income tax expense (benefit)	(8)	48	(19)	(481)
Earnings before equity in earnings of nonconsolidated subsidiaries	(242)	13	(160)	(1,018)
Equity in earnings of nonconsolidated subsidiaries	(37,918)	(22,658)	(100,555)	(77,735)
Net earnings	(38,160)	(22,645)	(100,715)	(78,753)
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	(38,160)	(22,645)	(100,715)	(78,753)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	284,538	261,928	893,988	837,137
Cost of sales	216,039	199,957	666,060	619,493
Gross profit	68,499	61,971	227,928	217,644
Selling, general and administrative expenses	46,451	46,183	143,590	133,207
Operating income	22,048	15,788	84,338	84,437
Other income (expense):
Interest expense	(10,884)	(10,920)	(32,672)	(32,768)
Interest income	268	68	563	181
Other	1,379	1,370	3,900	1,694
Total other income (expenses)	(9,237)	(9,482)	(28,209)	(30,893)
Earnings before income taxes	12,811	6,306	56,129	53,544
Income tax expense:
Current	9,030	6,112	19,487	22,086
Deferred income taxes	(3,474)	(5,321)	2,065	(1,834)
Total income tax expense (benefit)	5,556	791	21,552	20,252
Earnings before equity in earnings of nonconsolidated subsidiaries	7,255	5,515	34,577	33,292
Equity in earnings of nonconsolidated subsidiaries	27,953	22,658	85,274	69,876
Net earnings	35,208	28,173	119,851	103,168
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	35,208	28,173	119,851	103,168
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	113,243	89,305	352,827	277,990
Cost of sales	88,757	66,401	271,620	205,497
Gross profit	24,486	22,904	81,207	72,493
Selling, general and administrative expenses	12,046	11,073	35,555	33,583
Operating income	12,440	11,831	45,652	38,910
Other income (expense):
Interest expense	(3,989)	(6)	(10,040)	(9)
Interest income	9	12	33	51
Other	11	12	42	39
Total other income (expenses)	(3,969)	18	(9,965)	81
Earnings before income taxes	8,471	11,849	35,687	38,991
Income tax expense:
Current	3,082	5,095	13,184	13,909
Deferred income taxes	0	0	0	0
Total income tax expense (benefit)	3,082	5,095	13,184	13,909
Earnings before equity in earnings of nonconsolidated subsidiaries	5,389	6,754	22,503	25,082
Equity in earnings of nonconsolidated subsidiaries	9,965	0	15,281	7,859
Net earnings	15,354	6,754	37,784	32,941
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	15,354	6,754	37,784	32,941
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	343,818	300,648	967,130	873,673
Cost of sales	272,959	230,561	764,607	671,202
Gross profit	70,859	70,087	202,523	202,471
Selling, general and administrative expenses	45,174	44,527	129,619	136,908
Operating income	25,685	25,560	72,904	65,563
Other income (expense):
Interest expense	(306)	(174)	(640)	(499)
Interest income	5,023	691	12,649	2,057
Other	(873)	(504)	(2,258)	(1,281)
Total other income (expenses)	3,844	13	9,751	277
Earnings before income taxes	29,529	25,573	82,655	65,840
Income tax expense:
Current	9,059	6,762	17,612	15,762
Deferred income taxes	(3,794)	1,572	(1,986)	300
Total income tax expense (benefit)	5,265	8,334	15,626	16,062
Earnings before equity in earnings of nonconsolidated subsidiaries	24,264	17,239	67,029	49,778
Equity in earnings of nonconsolidated subsidiaries	0	0	0	0
Net earnings	24,264	17,239	67,029	49,778
Less: Earnings attributable to noncontrolling interests	(1,458)	(1,348)	(4,098)	(3,966)
Net earnings attributable to Valmont Industries, Inc.	$ 22,806	$ 15,891	$ 62,931	$ 45,812