ACQUISITIONS (Narrative) (Details) $ in Thousands					12 Months Ended
	Nov. 30, 2021 USD ($)	Nov. 03, 2021 USD ($)	Jul. 23, 2021 USD ($)	Apr. 02, 2021 USD ($) specialist	Dec. 31, 2022 USD ($) business	Dec. 31, 2021 USD ($) business	Dec. 31, 2020 USD ($) business
Business Acquisition [Line Items]
Contingent consideration					$ 2,645	$ 57,249	$ 7,119
PolSource
Business Acquisition [Line Items]
Equity interest acquired				100.00%
Number of specialists in acquired entity (more than) | specialist				350
Purchase price including contingent consideration				$ 148,200
Contingent consideration				35,400
Maximum amount of earnout payable				45,000
Revenue of acquiree						55,000
Acquisition related costs						1,400
Intangible assets				15,790
Amount				15,790
PolSource | Customer relationships
Business Acquisition [Line Items]
Amount				$ 14,790
CORE
Business Acquisition [Line Items]
Equity interest acquired			100.00%
Purchase price including contingent consideration			$ 50,200
Contingent consideration			4,000
Maximum amount of earnout payable			8,100
Deferred consideration			7,800
Revenue of acquiree						14,100
Acquisition related costs						1,200
Intangible assets			8,368
Amount			8,368
CORE | Customer relationships
Business Acquisition [Line Items]
Amount			$ 7,779
Emakina
Business Acquisition [Line Items]
Equity interest acquired	1.31%	98.69%
Cash consideration	$ 1,700	$ 143,400
Revenue of acquiree						24,700
Acquisition related costs						1,000
Intangible assets		30,488
Amount		30,488
Emakina | Customer relationships
Business Acquisition [Line Items]
Amount		$ 27,822
2020 Acquisitions purchase accounting adjustments
Business Acquisition [Line Items]
Contingent consideration							5,300
Maximum amount of earnout payable							18,600
Revenue of acquiree							$ 6,000
Number of completed acquisitions | business							2
Aggregate purchase price including contingent consideration at fair value at acquisition date							$ 22,500
Intangible assets							$ 7,300
Other 2021 Acquisitions
Business Acquisition [Line Items]
Contingent consideration						17,600
Maximum amount of earnout payable						30,200
Revenue of acquiree						$ 19,500
Number of completed acquisitions | business						4,000
Intangible assets						$ 14,100
Purchase price including contingent consideration						$ 65,200
Other 2021 Acquisitions | Minimum
Business Acquisition [Line Items]
Estimated future operating results, period						12 months
Other 2021 Acquisitions | Maximum
Business Acquisition [Line Items]
Estimated future operating results, period						48 months
2022 Acquisitions
Business Acquisition [Line Items]
Purchase price including contingent consideration					13,600
Contingent consideration					2,600
Revenue of acquiree					$ 8,700
Number of completed acquisitions | business					2
2022 Acquisitions | Customer relationships
Business Acquisition [Line Items]
Amount					$ 3,400