GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 24, 2016	Dec. 26, 2015
Current assets:
Cash and cash equivalents	$ 493,490	$ 399,948	$ 349,375	$ 349,074
Receivables, net	492,842	439,342
Inventories	403,234	350,028
Prepaid expenses, restricted cash, and other assets	50,064	57,297
Refundable income taxes	8,493	6,601
Total current assets	1,448,123	1,253,216
Property, plant and equipment, at cost	1,169,854	1,105,736
Less accumulated depreciation and amortization	647,430	587,401
Net property, plant and equipment	522,424	518,335
Goodwill	336,754	321,110
Other intangible assets	142,090	144,378
Investment in subsidiaries and intercompany accounts	0	0
Other assets	160,780	154,692
Total assets	2,610,171	2,391,731
Current liabilities:
Current installments of long-term debt	949	851
Notes payable to banks	197	746
Accounts payable	216,104	177,488
Accrued employee compensation and benefits	81,494	72,404
Accrued expenses	106,238	89,914
Dividends payable	8,478	8,445
Total current liabilities	(413,460)	(349,848)
Deferred income taxes	28,183	35,803
Long-term debt, excluding current installments	754,202	754,795
Defined benefit pension liability	199,562	209,470
Deferred compensation	48,612	44,319
Other noncurrent liabilities	13,557	14,910
Shareholders’ equity:
Common stock of $1 par value	27,900	27,900
Additional paid-in capital	0	0
Retained earnings	1,974,601	1,874,722
Accumulated other comprehensive loss	(288,102)	(346,359)
Treasury stock	(601,565)	(612,781)
Total Valmont Industries, Inc. shareholders’ equity	1,112,834	943,482
Noncontrolling interest in consolidated subsidiaries	39,761	39,104
Total shareholders’ equity	1,152,595	982,586	1,002,301	965,211
Total liabilities and shareholders’ equity	2,610,171	2,391,731
Eliminations
Current assets:
Cash and cash equivalents	0	0	0	0
Receivables, net	0	0
Inventories	(4,333)	(4,154)
Prepaid expenses, restricted cash, and other assets	0	0
Refundable income taxes	0	0
Total current assets	(4,333)	(4,154)
Property, plant and equipment, at cost	0	0
Less accumulated depreciation and amortization	0	0
Net property, plant and equipment	0	0
Goodwill	0	0
Other intangible assets	0	0
Investment in subsidiaries and intercompany accounts	(3,603,096)	(3,270,540)
Other assets	0	0
Total assets	(3,607,429)	(3,274,694)
Current liabilities:
Current installments of long-term debt	0	0
Notes payable to banks	0	0
Accounts payable	0	0
Accrued employee compensation and benefits	0	0
Accrued expenses	0	0
Dividends payable	0	0
Total current liabilities	0	0
Deferred income taxes	0	0
Long-term debt, excluding current installments	(192,465)	0
Defined benefit pension liability	0	0
Deferred compensation	0	0
Other noncurrent liabilities	0	0
Shareholders’ equity:
Common stock of $1 par value	(1,106,632)	(1,106,633)
Additional paid-in capital	(1,274,325)	(1,266,950)
Retained earnings	(1,320,815)	(1,250,087)
Accumulated other comprehensive loss	286,808	348,976
Treasury stock	0	0
Total Valmont Industries, Inc. shareholders’ equity	(3,414,964)	(3,274,694)
Noncontrolling interest in consolidated subsidiaries	0	0
Total shareholders’ equity	(3,414,964)	(3,274,694)
Total liabilities and shareholders’ equity	(3,607,429)	(3,274,694)
Parent
Current assets:
Cash and cash equivalents	118,499	67,225	47,301	62,281
Receivables, net	152,290	134,351
Inventories	141,774	126,669
Prepaid expenses, restricted cash, and other assets	8,903	13,271
Refundable income taxes	8,493	6,601
Total current assets	429,959	348,117
Property, plant and equipment, at cost	558,484	547,076
Less accumulated depreciation and amortization	369,620	352,960
Net property, plant and equipment	188,864	194,116
Goodwill	20,108	20,108
Other intangible assets	144	184
Investment in subsidiaries and intercompany accounts	1,392,533	1,279,413
Other assets	47,613	43,880
Total assets	2,079,221	1,885,818
Current liabilities:
Current installments of long-term debt	0	0
Notes payable to banks	0	0
Accounts payable	59,467	52,272
Accrued employee compensation and benefits	40,760	34,508
Accrued expenses	44,896	30,261
Dividends payable	8,478	8,445
Total current liabilities	(153,601)	(125,486)
Deferred income taxes	15,617	22,481
Long-term debt, excluding current installments	750,933	751,251
Defined benefit pension liability	0	0
Deferred compensation	43,077	39,476
Other noncurrent liabilities	3,159	3,642
Shareholders’ equity:
Common stock of $1 par value	27,900	27,900
Additional paid-in capital	0	0
Retained earnings	1,974,601	1,874,722
Accumulated other comprehensive loss	(288,102)	(346,359)
Treasury stock	(601,565)	(612,781)
Total Valmont Industries, Inc. shareholders’ equity	1,112,834	943,482
Noncontrolling interest in consolidated subsidiaries	0	0
Total shareholders’ equity	1,112,834	943,482
Total liabilities and shareholders’ equity	2,079,221	1,885,818
Guarantors
Current assets:
Cash and cash equivalents	4,167	6,071	5,818	4,008
Receivables, net	69,781	60,522
Inventories	46,747	45,457
Prepaid expenses, restricted cash, and other assets	1,023	880
Refundable income taxes	0	0
Total current assets	121,718	112,930
Property, plant and equipment, at cost	158,087	153,596
Less accumulated depreciation and amortization	82,708	76,776
Net property, plant and equipment	75,379	76,820
Goodwill	110,562	110,561
Other intangible assets	32,204	35,953
Investment in subsidiaries and intercompany accounts	1,180,732	901,758
Other assets	0	0
Total assets	1,520,595	1,238,022
Current liabilities:
Current installments of long-term debt	0	0
Notes payable to banks	0	0
Accounts payable	8,032	15,732
Accrued employee compensation and benefits	8,293	7,243
Accrued expenses	9,222	15,242
Dividends payable	0	0
Total current liabilities	(25,547)	(38,217)
Deferred income taxes	0	0
Long-term debt, excluding current installments	185,674	0
Defined benefit pension liability	0	0
Deferred compensation	0	0
Other noncurrent liabilities	5	5
Shareholders’ equity:
Common stock of $1 par value	457,950	457,950
Additional paid-in capital	166,789	159,414
Retained earnings	684,532	646,749
Accumulated other comprehensive loss	98	(64,313)
Treasury stock	0	0
Total Valmont Industries, Inc. shareholders’ equity	1,309,369	1,199,800
Noncontrolling interest in consolidated subsidiaries	0	0
Total shareholders’ equity	1,309,369	1,199,800
Total liabilities and shareholders’ equity	1,520,595	1,238,022
Non- Guarantors
Current assets:
Cash and cash equivalents	370,824	326,652	$ 296,256	$ 282,785
Receivables, net	270,771	244,469
Inventories	219,046	182,056
Prepaid expenses, restricted cash, and other assets	40,138	43,146
Refundable income taxes	0	0
Total current assets	900,779	796,323
Property, plant and equipment, at cost	453,283	405,064
Less accumulated depreciation and amortization	195,102	157,665
Net property, plant and equipment	258,181	247,399
Goodwill	206,084	190,441
Other intangible assets	109,742	108,241
Investment in subsidiaries and intercompany accounts	1,029,831	1,089,369
Other assets	113,167	110,812
Total assets	2,617,784	2,542,585
Current liabilities:
Current installments of long-term debt	949	851
Notes payable to banks	197	746
Accounts payable	148,605	109,484
Accrued employee compensation and benefits	32,441	30,653
Accrued expenses	52,120	44,411
Dividends payable	0	0
Total current liabilities	(234,312)	(186,145)
Deferred income taxes	12,566	13,322
Long-term debt, excluding current installments	10,060	3,544
Defined benefit pension liability	199,562	209,470
Deferred compensation	5,535	4,843
Other noncurrent liabilities	10,393	11,263
Shareholders’ equity:
Common stock of $1 par value	648,682	648,683
Additional paid-in capital	1,107,536	1,107,536
Retained earnings	636,283	603,338
Accumulated other comprehensive loss	(286,906)	(284,663)
Treasury stock	0	0
Total Valmont Industries, Inc. shareholders’ equity	2,105,595	2,074,894
Noncontrolling interest in consolidated subsidiaries	39,761	39,104
Total shareholders’ equity	2,145,356	2,113,998
Total liabilities and shareholders’ equity	$ 2,617,784	$ 2,542,585