BUSINESS SEGMENTS (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 24, 2016 USD ($)	Jun. 25, 2016 USD ($)	Mar. 26, 2016 USD ($)	Dec. 30, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 26, 2015 USD ($)
Business Segments
Number of reportable segments | segment									4
Maximum percentage of sales of other businesses and activities to consolidated sales as basis for aggregation									10.00%
Net sales	$ 714,978	$ 680,779	$ 712,737	$ 637,473	$ 674,575	$ 610,247	$ 640,249	$ 596,605	$ 2,745,967	$ 2,521,676	$ 2,618,924
Operating Income									266,432	243,504	131,695
Interest expense, net									(39,908)	(41,304)	(41,325)
Other									1,940	18,254	2,637
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									228,464	220,454	93,007
Total assets	2,602,250				2,391,731				2,602,250	2,391,731	2,392,382
Capital expenditures									55,266	57,920	45,468
Depreciation and amortization									84,957	82,417	91,144
Engineered Support Structures
Business Segments
Net sales									912,240	891,099	880,802
Operating Income									62,960	72,273	28,792
Total assets	846,881				776,161				846,881	776,161	790,004
Capital expenditures									16,433	13,313	12,415
Depreciation and amortization									27,637	27,824	30,775
Coatings Segment
Business Segments
Net sales									856,244	735,617	777,750
Operating Income									97,853	71,171	38,324
Total assets	597,231				544,015				597,231	544,015	569,205
Capital expenditures									14,012	7,969	13,467
Depreciation and amortization									25,079	24,639	27,305
Coatings
Business Segments
Net sales									256,811	243,877	255,473
Operating Income									50,179	46,596	27,369
Total assets	288,890				274,666				288,890	274,666	270,793
Capital expenditures									11,080	24,873	6,836
Depreciation and amortization									15,115	12,883	12,962
Other
Business Segments
Net sales									644,372	567,973	605,771
Operating Income									101,498	90,945	78,218
Total assets	369,798				313,982				369,798	313,982	310,967
Capital expenditures									7,055	8,836	7,756
Depreciation and amortization									11,173	12,097	11,746
Other
Business Segments
Net sales									76,300	83,110	99,128
Operating Income									2,134	8,730	(4,767)
Total assets	68,934				65,296				68,934	65,296	72,646
Capital expenditures									2,376	1,601	2,318
Depreciation and amortization									2,486	2,502	3,992
LIFO Adjustment [Member]
Business Segments
Operating Income									(5,680)	(2,972)	12,103
Corporate
Business Segments
Operating Income									(42,512)	(43,239)	(48,344)
Total assets	430,516				417,611				430,516	417,611	378,767
Capital expenditures									4,310	1,328	2,676
Depreciation and amortization									3,467	2,472	4,364
Parent
Business Segments
Net sales									1,200,181	1,126,985	1,169,674
Operating Income									109,200	104,876	85,097
Other									5,681	1,480	(2,374)
Earnings before income taxes and equity in earnings of nonconsolidated subsidiaries									72,077	62,926	39,180
Total assets	$ 2,089,253				$ 1,885,818				2,089,253	1,885,818
Capital expenditures									20,460	9,031	14,362
Depreciation and amortization									26,237	27,096	29,433
Operating segment
Business Segments
Sales									2,844,838	2,590,878	2,681,716
Operating segment | Engineered Support Structures
Business Segments
Sales									938,102	906,719	881,861
Operating segment | Engineered Support Structures | Lighting, Traffic, and Roadway Products
Business Segments
Sales									633,178	612,868	580,877
Operating segment | Engineered Support Structures | Communication Products
Business Segments
Sales									171,718	162,148	162,635
Operating segment | Engineered Support Structures | Access Systems
Business Segments
Sales									133,206	131,703	138,349
Operating segment | Coatings Segment
Business Segments
Sales									859,115	736,364	781,579
Operating segment | Coatings Segment | Offshore and Other Complex Steel Structures
Business Segments
Sales									100,773	107,824	103,068
Operating segment | Coatings Segment | Steel
Business Segments
Sales									658,604	538,284	582,930
Operating segment | Coatings Segment | Concrete
Business Segments
Sales									99,738	90,256	95,581
Operating segment | Coatings
Business Segments
Sales									318,891	289,481	302,385
Operating segment | Other
Business Segments
Sales									652,430	575,204	612,201
Operating segment | Other
Business Segments
Sales									76,300	83,110	103,690
Intersegment
Business Segments
Sales									98,871	69,202	62,792
Intersegment | Engineered Support Structures
Business Segments
Sales									25,862	15,620	1,059
Intersegment | Coatings Segment
Business Segments
Sales									2,871	747	3,829
Intersegment | Coatings
Business Segments
Sales									62,080	45,604	46,912
Intersegment | Other
Business Segments
Sales									8,058	7,231	6,430
Intersegment | Other
Business Segments
Sales									$ 0	$ 0	$ 4,562