GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Jun. 29, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Dec. 30, 2017
Current assets:
Cash and cash equivalents	$ 327,200		$ 313,210
Receivables, net	501,215		483,963
Inventories	377,300		383,566
Contract asset - costs and profits in excess of billings	120,376		112,525
Prepaid expenses and other assets	50,420		42,800
Refundable income taxes	11,893		4,576
Total current assets	1,388,404		1,340,640
Property, plant and equipment, at cost	1,233,762		1,160,865
Less accumulated depreciation and amortization	685,394		646,873
Net property, plant and equipment	548,368		513,992
Goodwill	421,679		385,207
Other intangible assets	177,734		175,956
Investment in subsidiaries and intercompany accounts	0		0
Other assets	189,257		114,479
Total assets	2,725,442		2,530,274
Current liabilities:
Current installments of long-term debt	745		779
Notes payable to banks	19,324		10,678
Accounts payable	197,535		218,115
Accrued employee compensation and benefits	78,540		79,291
Accrued expenses	226,715		91,942
Dividends payable	8,088		8,230
Total current liabilities	530,947		409,035
Deferred income taxes	43,778		43,489
Long-term debt, excluding current installments	764,524		741,822
Defined benefit pension liability	121,282		143,904
Deferred compensation	43,837		46,107
Other noncurrent liabilities	133,740		56,501
Shareholders’ equity:
Common stock of $1 par value	27,900		27,900
Additional paid-in capital	0		0
Retained earnings	2,119,843		2,027,596
Accumulated other comprehensive loss	(316,717)		(303,185)
Treasury stock	(744,335)		(692,549)
Total Valmont Industries, Inc. shareholders’ equity	1,086,691		1,059,762
Noncontrolling interest in consolidated subsidiaries	44,480		75,761
Total shareholders’ equity	1,131,171	$ 1,127,014	1,135,523	$ 1,133,748	$ 1,149,824	$ 1,151,795
Total liabilities and shareholders’ equity	2,725,442		2,530,274
Eliminations
Current assets:
Cash and cash equivalents	0		0
Receivables, net	0		0
Inventories	(2,942)		(2,402)
Contract asset - costs and profits in excess of billings	0		0
Prepaid expenses and other assets	0		0
Refundable income taxes	0		0
Total current assets	(2,942)		(2,402)
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	(3,313,199)		(3,381,139)
Other assets	0		0
Total assets	(3,316,141)		(3,383,541)
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	(119,716)		(166,729)
Defined benefit pension liability	0		0
Other noncurrent liabilities	0		0
Shareholders’ equity:
Common stock of $1 par value	(1,106,907)		(1,106,632)
Additional paid-in capital	(1,270,442)		(1,270,442)
Retained earnings	(1,150,041)		(1,092,093)
Accumulated other comprehensive loss	330,965		252,355
Treasury stock	0		0
Total Valmont Industries, Inc. shareholders’ equity	(3,196,425)		(3,216,812)
Noncontrolling interest in consolidated subsidiaries	0		0
Total shareholders’ equity	(3,196,425)		(3,216,812)
Total liabilities and shareholders’ equity	(3,316,141)		(3,383,541)
Parent
Current assets:
Cash and cash equivalents	179,765		104,256
Receivables, net	161,260		134,943
Inventories	125,240		138,158
Contract asset - costs and profits in excess of billings	58,713		50,271
Prepaid expenses and other assets	15,569		21,858
Refundable income taxes	11,893		4,576
Total current assets	552,440		454,062
Property, plant and equipment, at cost	614,979		579,046
Less accumulated depreciation and amortization	411,808		390,438
Net property, plant and equipment	203,171		188,608
Goodwill	20,108		20,108
Other intangible assets	36		76
Investment in subsidiaries and intercompany accounts	1,333,420		1,286,545
Other assets	78,721		47,674
Total assets	2,187,896		1,997,073
Current liabilities:
Current installments of long-term debt	0		0
Notes payable to banks	0		0
Accounts payable	64,256		68,304
Accrued employee compensation and benefits	41,371		41,418
Accrued expenses	162,640		25,936
Dividends payable	8,088		8,230
Total current liabilities	276,355		143,888
Deferred income taxes	16,645		14,376
Long-term debt, excluding current installments	734,417		733,964
Defined benefit pension liability	0		0
Other noncurrent liabilities	73,788		45,083
Shareholders’ equity:
Common stock of $1 par value	27,900		27,900
Additional paid-in capital	0		0
Retained earnings	2,119,843		2,027,596
Accumulated other comprehensive loss	(316,717)		(303,185)
Treasury stock	(744,335)		(692,549)
Total Valmont Industries, Inc. shareholders’ equity	1,086,691		1,059,762
Noncontrolling interest in consolidated subsidiaries	0		0
Total shareholders’ equity	1,086,691		1,059,762
Total liabilities and shareholders’ equity	2,187,896		1,997,073
Guarantors
Current assets:
Cash and cash equivalents	1,963		5,518
Receivables, net	79,077		75,204
Inventories	46,133		37,019
Contract asset - costs and profits in excess of billings	35,195		35,200
Prepaid expenses and other assets	4,866		746
Refundable income taxes	0		0
Total current assets	167,234		153,687
Property, plant and equipment, at cost	199,176		172,050
Less accumulated depreciation and amortization	100,692		93,374
Net property, plant and equipment	98,484		78,676
Goodwill	140,095		110,562
Other intangible assets	46,758		27,452
Investment in subsidiaries and intercompany accounts	1,138,854		1,161,612
Other assets	4,859		0
Total assets	1,596,284		1,531,989
Current liabilities:
Current installments of long-term debt	0		0
Notes payable to banks	0		0
Accounts payable	18,681		21,081
Accrued employee compensation and benefits	5,994		7,186
Accrued expenses	13,024		10,132
Dividends payable	0		0
Total current liabilities	37,699		38,399
Deferred income taxes	0		0
Long-term debt, excluding current installments	119,716		166,729
Defined benefit pension liability	0		0
Other noncurrent liabilities	3,622		620
Shareholders’ equity:
Common stock of $1 par value	457,950		457,950
Additional paid-in capital	162,906		162,906
Retained earnings	733,109		624,394
Accumulated other comprehensive loss	81,282		80,991
Treasury stock	0		0
Total Valmont Industries, Inc. shareholders’ equity	1,435,247		1,326,241
Noncontrolling interest in consolidated subsidiaries	0		0
Total shareholders’ equity	1,435,247		1,326,241
Total liabilities and shareholders’ equity	1,596,284		1,531,989
Non- Guarantors
Current assets:
Cash and cash equivalents	145,472		203,436
Receivables, net	260,878		273,816
Inventories	208,869		210,791
Contract asset - costs and profits in excess of billings	26,468		27,054
Prepaid expenses and other assets	29,985		20,196
Refundable income taxes	0		0
Total current assets	671,672		735,293
Property, plant and equipment, at cost	419,607		409,769
Less accumulated depreciation and amortization	172,894		163,061
Net property, plant and equipment	246,713		246,708
Goodwill	261,476		254,537
Other intangible assets	130,940		148,428
Investment in subsidiaries and intercompany accounts	840,925		932,982
Other assets	105,677		66,805
Total assets	2,257,403		2,384,753
Current liabilities:
Current installments of long-term debt	745		779
Notes payable to banks	19,324		10,678
Accounts payable	114,598		128,730
Accrued employee compensation and benefits	31,175		30,687
Accrued expenses	51,051		55,874
Dividends payable	0		0
Total current liabilities	216,893		226,748
Deferred income taxes	27,133		29,113
Long-term debt, excluding current installments	30,107		7,858
Defined benefit pension liability	121,282		143,904
Other noncurrent liabilities	56,330		10,798
Shareholders’ equity:
Common stock of $1 par value	648,957		648,682
Additional paid-in capital	1,107,536		1,107,536
Retained earnings	416,932		467,699
Accumulated other comprehensive loss	(412,247)		(333,346)
Treasury stock	0		0
Total Valmont Industries, Inc. shareholders’ equity	1,761,178		1,890,571
Noncontrolling interest in consolidated subsidiaries	44,480		75,761
Total shareholders’ equity	1,805,658		1,966,332
Total liabilities and shareholders’ equity	$ 2,257,403		$ 2,384,753