ACQUISITIONS (Narrative) (Details) $ in Thousands					3 Months Ended	12 Months Ended
	Nov. 30, 2021 USD ($)	Nov. 03, 2021 USD ($)	Jul. 23, 2021 USD ($)	Apr. 02, 2021 USD ($) specialist	Mar. 31, 2022 USD ($) business	Dec. 31, 2021 USD ($) business
PolSource S.A.
Business Acquisition [Line Items]
Percentage of voting interests acquired				100.00%
Number of specialists in acquired entity (more than) | specialist				350
Purchase price including contingent consideration				$ 148,200
Contingent consideration fair value				35,400
Maximum amount of earnout payable				45,000
Intangible assets				15,790
Finite-lived intangible assets acquired, amount				15,790
PolSource S.A. | Customer relationships
Business Acquisition [Line Items]
Finite-lived intangible assets acquired, amount				$ 14,790
CORE SE
Business Acquisition [Line Items]
Percentage of voting interests acquired			100.00%
Purchase price including contingent consideration			$ 50,200
Contingent consideration fair value			4,000
Maximum amount of earnout payable			8,100
Deferred consideration			7,800
Intangible assets			8,368
Finite-lived intangible assets acquired, amount			8,368
CORE SE | Customer relationships
Business Acquisition [Line Items]
Finite-lived intangible assets acquired, amount			$ 7,779
Emakina Group SA
Business Acquisition [Line Items]
Percentage of voting interests acquired	1.31%	98.69%
Fair value of contingent consideration					$ 400
Cash consideration	$ 1,700	$ 143,400
Intangible assets		30,488
Finite-lived intangible assets acquired, amount		30,488
Emakina Group SA | Customer relationships
Business Acquisition [Line Items]
Finite-lived intangible assets acquired, amount		$ 27,822
Other 2021 acquisitions purchase accounting adjustment
Business Acquisition [Line Items]
Contingent consideration fair value						$ 17,600
Maximum amount of earnout payable						$ 30,200
Number of acquisitions | business						4
Purchase price including contingent consideration						$ 65,200
Intangible assets						$ 14,100
Other 2021 acquisitions purchase accounting adjustment | Minimum
Business Acquisition [Line Items]
Estimated future operating results, period						12 months
Other 2021 acquisitions purchase accounting adjustment | Maximum
Business Acquisition [Line Items]
Estimated future operating results, period						48 months
2022 Acquisitions
Business Acquisition [Line Items]
Purchase price including contingent consideration					10,600
Contingent consideration fair value					$ 1,800
Number of acquisitions | business					1
2022 Acquisitions | Customer relationships
Business Acquisition [Line Items]
Finite-lived intangible assets acquired, amount					$ 2,300