ACQUISITIONS (Details) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
		Jul. 31, 2017		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 31, 2018
Acquisitions
Business Combination Receivable From Seller										$ 10,983
Sales Revenue, Goods, Net				$ 737,099		$ 669,491	$ 2,284,847	$ 1,877,246
Business Combination, Bargain Purchase, Gain Recognized, Amount				$ 0		$ (51,585)	0	(51,585)
Payments to Acquire Businesses, Net of Cash Acquired							$ (6,591)	$ 72,468
Air Liquide Welding [Member]
Acquisitions
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		$ 89,442
Indefinite-Lived Intangible Assets (Excluding Goodwill)		7,099
Business Combination, Bargain Purchase, Gain Recognized, Amount		(49,650)	[1]		$ 1,935
Business Combination, Recognized Identifiable Other Assets Acquired and Other Liabilities Assumed, Net	[2]	(27,210)
Business Combination, Consideration Transferred		135,123
Payments to Acquire Businesses, Net of Cash Acquired		61,953	[3]						$ 61,953
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	[4]	97,803
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	[5]	73,056
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	[6]	11,715
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		(65,640)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Pension Liability		$ (67,563)
Trademarks and Trade Names [Member] | Air Liquide Welding [Member]
Acquisitions
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		10 years
Other Intangible Assets, Net		$ 1,183
Other Intangible Assets [Member] | Air Liquide Welding [Member]
Acquisitions
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		9 years
Other Intangible Assets, Net		$ 3,433

[1] An adjustment of $1,935 was recorded to the Bargain purchase gain in the fourth quarter of 2017.

[2] Consists primarily of other accrued liabilities.

[3] Reflects a receivable from seller for an agreed upon purchase price adjustment. The payment of $10,983 was received in the first quarter of 2018.

[4] nventories acquired were sold in the third quarter of 2017 resulting in a $2,314 increase in Cost of goods sold for the amortization of step up in the value of acquired inventories.

[5] Property, plant and equipment acquired includes a number of manufacturing and distribution sites, including the related facilities, land and leased sites, and machinery and equipment for use in manufacturing operations.

[6] $7,099 of the intangible asset balance was assigned to a trade name expected to have an indefinite life. Of the remaining amount, $1,183 was assigned to a finite-lived trade name (10 year weighted average useful life) and $3,433 was assigned to other intangible assets (9 year weighted average life).