GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Statements of Earnings (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019 USD ($) tranche	Sep. 29, 2018 USD ($)	Sep. 28, 2019 USD ($) tranche	Sep. 29, 2018 USD ($)
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	$ 690,340	$ 678,692	$ 2,083,350	$ 2,059,781
Cost of sales	514,254	514,352	1,561,721	1,551,202
Gross profit	176,086	164,340	521,629	508,579
Selling, general and administrative expenses	112,223	125,980	338,950	342,589
Operating income	63,863	38,360	182,679	165,990
Other income (expense):
Interest expense	(9,976)	(10,954)	(29,971)	(33,819)
Interest income	969	1,000	2,815	3,713
Other	1,170	(12,324)	6,692	(17,705)
Total other income (expenses)	(7,837)	(22,278)	(20,464)	(47,811)
Earnings before income taxes	56,026	16,082	162,215	118,179
Income tax expense (benefit):
Deferred income taxes	1,388	(1,686)	7,098	814
Total income tax expense (benefit)	13,763	9,091	40,151	36,028
Earnings before equity in earnings of nonconsolidated subsidiaries	42,263	6,991	122,064	82,151
Equity in earnings in nonconsolidated subsidiaries	0	0	0	0
Net earnings	42,263	6,991	122,064	82,151
Less: Earnings attributable to noncontrolling interests	(2,119)	(2,543)	(4,042)	(5,462)
Net earnings attributable to Valmont Industries, Inc.	40,144	4,448	118,022	76,689
Eliminations
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	(58,189)	(65,566)	(184,620)	(200,754)
Cost of sales	(57,822)	(65,598)	(184,080)	(202,030)
Gross profit	(367)	32	(540)	1,276
Selling, general and administrative expenses	0	0	0	0
Operating income	(367)	32	(540)	1,276
Other income (expense):
Interest expense	2,543	3,600	8,583	11,229
Interest income	(2,543)	(3,600)	(8,583)	(11,229)
Other	0	0	0	0
Total other income (expenses)	0	0	0	0
Earnings before income taxes	(367)	32	(540)	1,276
Income tax expense (benefit):
Deferred income taxes			0	0
Total income tax expense (benefit)	(85)	(26)	(76)	62
Earnings before equity in earnings of nonconsolidated subsidiaries	(282)	58	(464)	1,214
Equity in earnings in nonconsolidated subsidiaries	(41,114)	(13,650)	(92,692)	(93,426)
Net earnings	(41,396)	(13,592)	(93,156)	(92,212)
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	(41,396)	(13,592)	(93,156)	(92,212)
Parent
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	302,461	293,070	915,436	906,978
Cost of sales	223,949	227,467	675,093	683,740
Gross profit	78,512	65,603	240,343	223,238
Selling, general and administrative expenses	67,366	51,159	175,000	147,949
Operating income	11,146	14,444	65,343	75,289
Other income (expense):
Interest expense	(9,471)	(10,511)	(28,638)	(32,788)
Interest income	607	174	1,060	655
Other	849	(13,765)	6,264	(15,773)
Total other income (expenses)	(8,015)	(24,102)	(21,314)	(47,906)
Earnings before income taxes	3,131	(9,658)	44,029	27,383
Income tax expense (benefit):
Deferred income taxes			3,869	729
Total income tax expense (benefit)	2,084	(4,497)	9,856	6,181
Earnings before equity in earnings of nonconsolidated subsidiaries	1,047	(5,161)	34,173	21,202
Equity in earnings in nonconsolidated subsidiaries	39,097	9,609	83,849	55,487
Net earnings	40,144	4,448	118,022	76,689
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	40,144	4,448	118,022	76,689
Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	135,392	132,059	413,050	386,793
Cost of sales	96,566	100,130	307,209	293,238
Gross profit	38,826	31,929	105,841	93,555
Selling, general and administrative expenses	2,325	12,908	28,301	37,360
Operating income	36,501	19,021	77,540	56,195
Other income (expense):
Interest expense	(2,544)	(3,600)	(8,583)	(11,229)
Interest income	2	47	32	62
Other	12	15	33	41
Total other income (expenses)	(2,530)	(3,538)	(8,518)	(11,126)
Earnings before income taxes	33,971	15,483	69,022	45,069
Income tax expense (benefit):
Deferred income taxes			0	1,791
Total income tax expense (benefit)	8,834	4,732	16,691	12,260
Earnings before equity in earnings of nonconsolidated subsidiaries	25,137	10,751	52,331	32,809
Equity in earnings in nonconsolidated subsidiaries	2,017	4,041	8,843	37,939
Net earnings	27,154	14,792	61,174	70,748
Less: Earnings attributable to noncontrolling interests	0	0	0	0
Net earnings attributable to Valmont Industries, Inc.	27,154	14,792	61,174	70,748
Non- Guarantors
Condensed consolidated financial information for the Company (Parent), the guarantor subsidiaries and the non-guarantor subsidiaries
Net sales	310,676	319,129	939,484	966,764
Cost of sales	251,561	252,353	763,499	776,254
Gross profit	59,115	66,776	175,985	190,510
Selling, general and administrative expenses	42,532	61,913	135,649	157,280
Operating income	16,583	4,863	40,336	33,230
Other income (expense):
Interest expense	(504)	(443)	(1,333)	(1,031)
Interest income	2,903	4,379	10,306	14,225
Other	309	1,426	395	(1,973)
Total other income (expenses)	2,708	5,362	9,368	11,221
Earnings before income taxes	19,291	10,225	49,704	44,451
Income tax expense (benefit):
Deferred income taxes			3,229	(1,706)
Total income tax expense (benefit)	2,930	8,882	13,680	17,525
Earnings before equity in earnings of nonconsolidated subsidiaries	16,361	1,343	36,024	26,926
Equity in earnings in nonconsolidated subsidiaries	0	0	0	0
Net earnings	16,361	1,343	36,024	26,926
Less: Earnings attributable to noncontrolling interests	(2,119)	(2,543)	(4,042)	(5,462)
Net earnings attributable to Valmont Industries, Inc.	$ 14,242	$ (1,200)	$ 31,982	$ 21,464