CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Statement of Comprehensive Income [Abstract]
Net earnings	$ 122,319	$ 178,391	$ 45,333
Foreign currency translation adjustments:
Unrealized translation gains (losses)	79,279	(58,315)	(96,694)
Gain/(loss) on hedging activities:
Unrealized gain (loss) on net investment hedge, net of tax expense (benefit) of ($880) in 2017 and $2,646 in 2016	(1,695)	4,226	0
Amortization cost included in interest expense	74	74	74
Realized (gain) loss included in net earnings	0	0	(3,130)
Unrealized gain (loss) on cash flow hedge	0	0	2,855
Derivative adjustment	(1,621)	4,300	(201)
Actuarial gain (loss) in defined benefit pension plan, net of tax expense (benefit) of ($10,732) in 2015, ($3,450) in 2014, and ($10,143) in 2013	(10,871)	(24,141)	(40,274)
Other comprehensive income (loss)	66,787	(78,156)	(137,169)
Comprehensive income (loss)	189,106	100,235	(91,836)
Comprehensive loss (income) attributable to noncontrolling interests	(5,529)	(6,144)	(832)
Comprehensive income (loss) attributable to Valmont Industries, Inc.	$ 183,577	$ 94,091	$ (92,668)