GUARANTOR/NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 30, 2019	Dec. 29, 2018	Mar. 31, 2018	Dec. 30, 2017
Current assets:
Cash and cash equivalents	$ 211,237	$ 313,210
Receivables, net	512,852	483,963
Inventories	395,799	383,566
Contract asset - costs and profits in excess of billings	119,886	112,525
Prepaid expenses and other assets	54,379	42,800
Refundable income taxes	4,747	4,576
Total current assets	1,298,900	1,340,640
Property, plant and equipment, at cost	1,196,633	1,160,865
Less accumulated depreciation and amortization	669,304	646,873
Net property, plant and equipment	527,329	513,992
Goodwill	416,996	385,207
Other intangible assets	192,897	175,956
Investment in subsidiaries and intercompany accounts	0	0
Other assets	209,865	114,479
Total assets	2,645,987	2,530,274
Current liabilities:
Current installments of long-term debt	764	779
Notes payable to banks	19,816	10,678
Accounts payable	219,460	218,115
Accrued employee compensation and benefits	63,425	79,291
Accrued expenses	129,161	91,942
Dividends payable	8,213	8,230
Total current liabilities	440,839	409,035
Deferred income taxes	46,440	43,489
Long-term debt, excluding current installments	741,629	741,822
Defined benefit pension liability	133,761	143,904
Other noncurrent liabilities	152,103	56,501
Shareholders’ equity:
Common stock of $1 par value	27,900	27,900
Additional paid-in capital	0	0
Retained earnings	2,049,438	2,027,596
Accumulated other comprehensive loss	(298,740)	(303,185)
Treasury stock	(700,333)	(692,549)
Total Valmont Industries, Inc. shareholders’ equity	1,078,265	1,059,762
Noncontrolling interest in consolidated subsidiaries	52,950	75,761
Total shareholders’ equity	1,131,215	1,135,523	$ 1,185,356	$ 1,151,795
Total liabilities and shareholders’ equity	2,645,987	2,530,274
Eliminations
Current assets:
Cash and cash equivalents	0	0
Receivables, net	0	0
Inventories	(2,027)	(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	(2,027)	(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	(3,645,535)	(3,381,139)
Other assets	0	0
Total assets	(3,647,562)	(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	(125,685)	(166,729)
Defined benefit pension liability	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)	(1,270,442)
Retained earnings	(1,444,774)	(1,092,093)
Accumulated other comprehensive loss	299,971	252,355
Treasury stock	0	0
Total Valmont Industries, Inc. shareholders’ equity	(3,521,877)	(3,216,812)
Noncontrolling interest in consolidated subsidiaries	0	0
Total shareholders’ equity	(3,521,877)	(3,216,812)
Total liabilities and shareholders’ equity	(3,647,562)	(3,383,541)
Parent
Current assets:
Cash and cash equivalents	58,146	104,256
Receivables, net	148,952	134,943
Inventories	133,792	138,158
Contract asset - costs and profits in excess of billings	58,485	50,271
Prepaid expenses and other assets	12,288	21,858
Refundable income taxes	4,747	4,576
Total current assets	416,410	454,062
Property, plant and equipment, at cost	590,577	579,046
Less accumulated depreciation and amortization	398,031	390,438
Net property, plant and equipment	192,546	188,608
Goodwill	20,108	20,108
Other intangible assets	63	76
Investment in subsidiaries and intercompany accounts	1,336,332	1,286,545
Other assets	99,721	47,674
Total assets	2,065,180	1,997,073
Current liabilities:
Current installments of long-term debt	0	0
Notes payable to banks	0	0
Accounts payable	63,348	68,304
Accrued employee compensation and benefits	30,829	41,418
Accrued expenses	44,779	25,936
Dividends payable	8,213	8,230
Total current liabilities	147,169	143,888
Deferred income taxes	18,505	14,376
Long-term debt, excluding current installments	734,114	733,964
Defined benefit pension liability	0	0
Other noncurrent liabilities	87,127	45,083
Shareholders’ equity:
Common stock of $1 par value	27,900	27,900
Additional paid-in capital	0	0
Retained earnings	2,049,438	2,027,596
Accumulated other comprehensive loss	(298,740)	(303,185)
Treasury stock	(700,333)	(692,549)
Total Valmont Industries, Inc. shareholders’ equity	1,078,265	1,059,762
Noncontrolling interest in consolidated subsidiaries	0	0
Total shareholders’ equity	1,078,265	1,059,762
Total liabilities and shareholders’ equity	2,065,180	1,997,073
Guarantors
Current assets:
Cash and cash equivalents	7,731	5,518
Receivables, net	91,153	75,204
Inventories	38,993	37,019
Contract asset - costs and profits in excess of billings	35,086	35,200
Prepaid expenses and other assets	13,079	746
Refundable income taxes	0	0
Total current assets	186,042	153,687
Property, plant and equipment, at cost	188,120	172,050
Less accumulated depreciation and amortization	101,322	93,374
Net property, plant and equipment	86,798	78,676
Goodwill	140,775	110,562
Other intangible assets	47,561	27,452
Investment in subsidiaries and intercompany accounts	1,031,430	1,161,612
Other assets	4,028	0
Total assets	1,496,634	1,531,989
Current liabilities:
Current installments of long-term debt	0	0
Notes payable to banks	0	0
Accounts payable	22,967	21,081
Accrued employee compensation and benefits	4,633	7,186
Accrued expenses	9,516	10,132
Dividends payable	0	0
Total current liabilities	37,116	38,399
Deferred income taxes	0	0
Long-term debt, excluding current installments	125,685	166,729
Defined benefit pension liability	0	0
Other noncurrent liabilities	3,440	620
Shareholders’ equity:
Common stock of $1 par value	457,950	457,950
Additional paid-in capital	162,906	162,906
Retained earnings	634,175	624,394
Accumulated other comprehensive loss	75,362	80,991
Treasury stock	0	0
Total Valmont Industries, Inc. shareholders’ equity	1,330,393	1,326,241
Noncontrolling interest in consolidated subsidiaries	0	0
Total shareholders’ equity	1,330,393	1,326,241
Total liabilities and shareholders’ equity	1,496,634	1,531,989
Non- Guarantors
Current assets:
Cash and cash equivalents	145,360	203,436
Receivables, net	272,747	273,816
Inventories	225,041	210,791
Contract asset - costs and profits in excess of billings	26,315	27,054
Prepaid expenses and other assets	29,012	20,196
Refundable income taxes	0	0
Total current assets	698,475	735,293
Property, plant and equipment, at cost	417,936	409,769
Less accumulated depreciation and amortization	169,951	163,061
Net property, plant and equipment	247,985	246,708
Goodwill	256,113	254,537
Other intangible assets	145,273	148,428
Investment in subsidiaries and intercompany accounts	1,277,773	932,982
Other assets	106,116	66,805
Total assets	2,731,735	2,384,753
Current liabilities:
Current installments of long-term debt	764	779
Notes payable to banks	19,816	10,678
Accounts payable	133,145	128,730
Accrued employee compensation and benefits	27,963	30,687
Accrued expenses	74,866	55,874
Dividends payable	0	0
Total current liabilities	256,554	226,748
Deferred income taxes	27,935	29,113
Long-term debt, excluding current installments	7,515	7,858
Defined benefit pension liability	133,761	143,904
Other noncurrent liabilities	61,536	10,798
Shareholders’ equity:
Common stock of $1 par value	648,682	648,682
Additional paid-in capital	1,107,536	1,107,536
Retained earnings	810,599	467,699
Accumulated other comprehensive loss	(375,333)	(333,346)
Treasury stock	0	0
Total Valmont Industries, Inc. shareholders’ equity	2,191,484	1,890,571
Noncontrolling interest in consolidated subsidiaries	52,950	75,761
Total shareholders’ equity	2,244,434	1,966,332
Total liabilities and shareholders’ equity	$ 2,731,735	$ 2,384,753