GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017	Dec. 31, 2017	Dec. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 479,663	$ 425,216		$ 492,805	$ 412,516
Receivables, net	467,010			503,677
Inventories	370,005		$ 384,705	420,948
Prepaid expenses and other assets	127,251		95,150	43,643
Assets Held-for-sale, Not Part of Disposal Group, Current	72,665
Refundable income taxes	6,749			11,492
Assets held for sale				11,492
Total current assets	1,523,343			1,472,565
Property, plant and equipment, at cost	1,137,152			1,165,687
Less accumulated depreciation and amortization	633,440			646,759
Net property, plant and equipment	503,712			518,928
Goodwill	327,874			337,720
Other intangible assets	129,540			138,599
Investment in subsidiaries and intercompany accounts	0			0
Other assets	133,595			134,438
Total assets	2,618,064			2,602,250
Current liabilities:
Current installments of long-term debt	951			966
Notes payable to banks	377			161
Accounts payable	190,902			227,906
Accrued employee compensation and benefits	67,928			84,426
Accrued expenses	92,651		83,072	81,029
Disposal Group, Including Discontinued Operations, Liabilities	12,960
Payments of Ordinary Dividends, Common Stock	8,510	8,445
Liabilities held for sale	8,493			8,510
Total current liabilities	(374,262)			(402,998)
Deferred income taxes	39,669		38,356	34,906
Long-term debt, excluding current installments	753,647			753,888
Defined benefit pension liability	195,490			189,552
Deferred compensation	48,597			48,526
Other noncurrent liabilities	21,043			20,585
Shareholders’ equity:
Common stock of $1 par value	27,900			27,900
Additional paid-in capital	0			0
Retained earnings	1,996,474		$ 1,964,115	1,954,344
Accumulated other comprehensive loss	(276,629)			(279,022)
Treasury stock	(602,504)			(590,386)
Total Valmont Industries, Inc. shareholders’ equity	1,145,241			1,112,836
Noncontrolling interest in consolidated subsidiaries	40,115			38,959
Total shareholders’ equity	1,185,356	1,041,280		1,151,795	982,586
Total liabilities and shareholders’ equity	2,618,064			2,602,250
Eliminations
Current assets:
Cash and cash equivalents	0	0		0	0
Receivables, net	0			0
Inventories	(2,700)			(3,848)
Prepaid expenses and other assets	0			0
Assets Held-for-sale, Not Part of Disposal Group, Current	0
Refundable income taxes	0
Assets held for sale				0
Total current assets	(2,700)			(3,848)
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	(3,555,831)			(3,525,162)
Other assets	0			0
Total assets	(3,558,531)			(3,529,010)
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
Disposal Group, Including Discontinued Operations, Liabilities	0
Payments of Ordinary Dividends, Common Stock	0	0
Liabilities held for sale	0			0
Total current liabilities	0			0
Deferred income taxes	0			0
Long-term debt, excluding current installments	(188,724)			(191,847)
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)			(1,106,632)
Additional paid-in capital	(1,270,442)			(1,266,950)
Retained earnings	(1,264,014)			(1,241,666)
Accumulated other comprehensive loss	271,281			278,085
Treasury stock	0			0
Total Valmont Industries, Inc. shareholders’ equity	(3,369,807)			(3,337,163)
Noncontrolling interest in consolidated subsidiaries	0			0
Total shareholders’ equity	(3,369,807)			(3,337,163)
Total liabilities and shareholders’ equity	(3,558,531)			(3,529,010)
Parent
Current assets:
Cash and cash equivalents	71,423	93,149		83,329	67,225
Receivables, net	139,677			149,221
Inventories	135,973			160,444
Prepaid expenses and other assets	42,926			8,607
Assets Held-for-sale, Not Part of Disposal Group, Current	0
Refundable income taxes	6,749
Assets held for sale				11,492
Total current assets	396,748			413,093
Property, plant and equipment, at cost	560,719			557,371
Less accumulated depreciation and amortization	374,716			368,668
Net property, plant and equipment	186,003			188,703
Goodwill	20,108			20,108
Other intangible assets	117			130
Investment in subsidiaries and intercompany accounts	1,430,127			1,416,446
Other assets	50,467			50,773
Total assets	2,083,570			2,089,253
Current liabilities:
Current installments of long-term debt	0			0
Notes payable to banks	0			0
Accounts payable	51,996			69,915
Accrued employee compensation and benefits	33,685			44,086
Accrued expenses	37,633			28,198
Disposal Group, Including Discontinued Operations, Liabilities	0
Payments of Ordinary Dividends, Common Stock	8,510	8,445
Liabilities held for sale	8,493			8,510
Total current liabilities	(131,807)			(150,709)
Deferred income taxes	925			20,885
Long-term debt, excluding current installments	750,705			750,821
Defined benefit pension liability	0			0
Deferred compensation	42,988			42,928
Other noncurrent liabilities	11,904			11,074
Shareholders’ equity:
Common stock of $1 par value	27,900			27,900
Additional paid-in capital	0			0
Retained earnings	1,996,474			1,954,344
Accumulated other comprehensive loss	(276,629)			(279,022)
Treasury stock	(602,504)			(590,386)
Total Valmont Industries, Inc. shareholders’ equity	1,145,241			1,112,836
Noncontrolling interest in consolidated subsidiaries	0			0
Total shareholders’ equity	1,145,241			1,112,836
Total liabilities and shareholders’ equity	2,083,570			2,089,253
Guarantors
Current assets:
Cash and cash equivalents	3,409	5,479		5,304	6,071
Receivables, net	67,545			82,995
Inventories	38,734			46,801
Prepaid expenses and other assets	37,527			970
Assets Held-for-sale, Not Part of Disposal Group, Current	0
Refundable income taxes	0
Assets held for sale				0
Total current assets	147,215			136,070
Property, plant and equipment, at cost	165,996			160,767
Less accumulated depreciation and amortization	87,080			84,508
Net property, plant and equipment	78,916			76,259
Goodwill	110,562			110,562
Other intangible assets	30,057			30,955
Investment in subsidiaries and intercompany accounts	1,178,134			1,181,537
Other assets	0			0
Total assets	1,544,884			1,535,383
Current liabilities:
Current installments of long-term debt	0			0
Notes payable to banks	0			0
Accounts payable	14,047			18,039
Accrued employee compensation and benefits	5,623			8,749
Accrued expenses	6,571			9,621
Disposal Group, Including Discontinued Operations, Liabilities	0
Payments of Ordinary Dividends, Common Stock	0	0
Liabilities held for sale	0			0
Total current liabilities	(26,241)			(36,409)
Deferred income taxes	16,883			0
Long-term debt, excluding current installments	182,065			185,078
Defined benefit pension liability	0			0
Deferred compensation	0			0
Other noncurrent liabilities	5			6
Shareholders’ equity:
Common stock of $1 par value	457,950			457,950
Additional paid-in capital	162,906			159,414
Retained earnings	633,032			622,044
Accumulated other comprehensive loss	65,802			74,482
Treasury stock	0			0
Total Valmont Industries, Inc. shareholders’ equity	1,319,690			1,313,890
Noncontrolling interest in consolidated subsidiaries	0			0
Total shareholders’ equity	1,319,690			1,313,890
Total liabilities and shareholders’ equity	1,544,884			1,535,383
Non- Guarantors
Current assets:
Cash and cash equivalents	404,831	326,588		404,172	$ 339,220
Receivables, net	259,788			271,461
Inventories	197,998			217,551
Prepaid expenses and other assets	46,798			34,066
Assets Held-for-sale, Not Part of Disposal Group, Current	72,665
Refundable income taxes	0
Assets held for sale				0
Total current assets	982,080			927,250
Property, plant and equipment, at cost	410,437			447,549
Less accumulated depreciation and amortization	171,644			193,583
Net property, plant and equipment	238,793			253,966
Goodwill	197,204			207,050
Other intangible assets	99,366			107,514
Investment in subsidiaries and intercompany accounts	947,570			927,179
Other assets	83,128			83,665
Total assets	2,548,141			2,506,624
Current liabilities:
Current installments of long-term debt	951			966
Notes payable to banks	377			161
Accounts payable	124,859			139,952
Accrued employee compensation and benefits	28,620			31,591
Accrued expenses	48,447			43,210
Disposal Group, Including Discontinued Operations, Liabilities	12,960
Payments of Ordinary Dividends, Common Stock	0	$ 0
Liabilities held for sale	0			0
Total current liabilities	(216,214)			(215,880)
Deferred income taxes	21,861			14,021
Long-term debt, excluding current installments	9,601			9,836
Defined benefit pension liability	195,490			189,552
Deferred compensation	5,609			5,598
Other noncurrent liabilities	9,134			9,505
Shareholders’ equity:
Common stock of $1 par value	648,682			648,682
Additional paid-in capital	1,107,536			1,107,536
Retained earnings	630,982			619,622
Accumulated other comprehensive loss	(337,083)			(352,567)
Treasury stock	0			0
Total Valmont Industries, Inc. shareholders’ equity	2,050,117			2,023,273
Noncontrolling interest in consolidated subsidiaries	40,115			38,959
Total shareholders’ equity	2,090,232			2,062,232
Total liabilities and shareholders’ equity	$ 2,548,141			$ 2,506,624