ACQUISITIONS - Narrative (Details) $ in Thousands	1 Months Ended													3 Months Ended								9 Months Ended	12 Months Ended			24 Months Ended
	Nov. 30, 2018 USD ($) facility	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Feb. 28, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($) facility	Sep. 30, 2017 USD ($)	Jul. 31, 2017 USD ($)	Apr. 30, 2017 USD ($) company	Mar. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jul. 01, 2018 USD ($)	Apr. 01, 2018 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) acquisition	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Number of businesses acquired | acquisition																							3
Revenues														$ 549,460	$ 566,186	$ 613,218	$ 608,218	$ 531,211	$ 575,139	$ 604,879	$ 551,832		$ 2,337,082	$ 2,263,061	$ 1,635,653
Operating income																							154,442	178,415	121,900
Contingent consideration liability														9,600				13,800					9,600	13,800		$ 9,600
Contingent consideration high value outcome														17,200									17,200			17,200
Payment for contingent consideration liability, financing activities																						$ 4,400	4,416	0	0
Decrease to contingent consideration liability																							3,100
Accretion expense																							700
Payments to acquire businesses, net of cash acquired																							55,953	343,347	251,851
Pro forma amortization expense																							1,300	7,000
Acquired Entities
Business Acquisition [Line Items]
Revenues																							8,300	249,300	109,700
Operating income																							900	23,200	13,100
G.G. Schmitt & Sons, Inc.
Business Acquisition [Line Items]
Contingent consideration liability														2,600									2,600			2,600
Consideration transferred																							54,300
Contingent consideration liability performance period							1 year
Metal Moulding Corporation
Business Acquisition [Line Items]
Contingent consideration liability																		1,400						1,400
Consideration transferred							$ 19,900
Contingent consideration liability performance period							1 year
Payments to acquire businesses, net of cash acquired																								19,900
Aluminum Metals Company
Business Acquisition [Line Items]
Consideration transferred							$ 17,800
Indiana Marine Products
Business Acquisition [Line Items]
Contingent consideration liability																		7,900						7,900
Consideration transferred						$ 18,600
Contingent consideration liability performance period						3 years
Payments to acquire businesses, net of cash acquired																								18,600
Collins & Company
Business Acquisition [Line Items]
Consideration transferred						$ 40,000
Provisional information adjustment, increase (decrease) intangible assets																							(3,600)
Goodwill adjustment increase (decrease)																							3,600
Dehco Inc
Business Acquisition [Line Items]
Consideration transferred					$ 52,800
Provisional information adjustment, increase (decrease) intangible assets																								(300)
Goodwill adjustment increase (decrease)																								300
Dowco Inc.
Business Acquisition [Line Items]
Consideration transferred				$ 56,300
Accounts payable																								100
Property plant and equipment adjustment increase (decrease)																								2,700
Provisional information adjustment, increase (decrease) intangible assets																								5,900
Increase (decrease) in initial purchase price																								3,300
Marine Accessories Corporation
Business Acquisition [Line Items]
Consideration transferred			$ 57,000
Property plant and equipment adjustment increase (decrease)																								1,000
Provisional information adjustment, increase (decrease) intangible assets																								6,500
Business combination, provisional information, adjustment, financial liabilities																								1,100
Percent of common stock acquired			100.00%
Increase (decrease) in initial purchase price																								6,400
Engineered Metals And Composites
Business Acquisition [Line Items]
Contingent consideration liability																		2,500						2,500
Accounts payable																								200
Contingent consideration liability performance period		3 months
Property plant and equipment adjustment increase (decrease)																								800
Goodwill adjustment																								600
Provisional information adjustment, increase (decrease) intangible assets																								1,600
Payments to acquire businesses, net of cash acquired		$ 25,300																					100	25,200		25,300
Increase (decrease) in working capital																								100
Increase (decrease) in initial purchase price																								100
Inventory adjustment increase (decrease)																								100
LaSalle Bristol
Business Acquisition [Line Items]
Consideration transferred	$ 51,500
Property plant and equipment adjustment increase (decrease)																								(800)
Number of manufacturing and distribution centers | facility	15
Provisional information adjustment, increase (decrease) intangible assets																								6,700
Goodwill adjustment increase (decrease)																								800
Increase (decrease) in initial purchase price																								1,500
Accounts payable and accrued liabilities adjustment increase (decrease)																								300
Accounts receivable adjustment increase (decrease)																								(700)
Inventory adjustment increase (decrease)																								(6,700)
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Deferred Tax Liability																								(800)
Increase (decrease) in prepaid expense																								300
Medallion
Business Acquisition [Line Items]
Consideration transferred													$ 9,900
LPE
Business Acquisition [Line Items]
Consideration transferred												$ 73,300
Percent of common stock acquired												100.00%
Number of manufacturing companies | company												3
Wire Design
Business Acquisition [Line Items]
Consideration transferred											$ 10,800
Baymont
Business Acquisition [Line Items]
Contingent consideration liability								$ 4,000																	4,000
Consideration transferred										$ 3,800
Contingent consideration liability performance period										6 years
Payments to acquire businesses, net of cash acquired																									$ 3,800
Indiana Transport
Business Acquisition [Line Items]
Consideration transferred									$ 58,800
LMI
Business Acquisition [Line Items]
Consideration transferred									$ 80,300
Number of manufacturing and distribution centers | facility									6
Nickell
Business Acquisition [Line Items]
Consideration transferred								$ 12,600
Accrued Liabilities
Business Acquisition [Line Items]
Contingent consideration liability														2,000				4,400					2,000	4,400		2,000
Other Noncurrent Liabilities
Business Acquisition [Line Items]
Contingent consideration liability														$ 7,600				$ 9,400					$ 7,600	$ 9,400		$ 7,600