INTANGIBLE ASSETS AND GOODWILL - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 482,558		$ 455,206
Minimum
Finite-Lived Intangible Assets [Line Items]
Percentage of fair value in excess of carrying amount	8.00%
Maximum
Finite-Lived Intangible Assets [Line Items]
Percentage of fair value in excess of carrying amount	65.00%
Advanced Plan Administration
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 88,900
Supplemental Benefits Administration
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 190,200
Percentage of fair value in excess of carrying amount	8.40%
Value Based Analytics
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 138,200
Percentage of fair value in excess of carrying amount	12.50%
HealthSmart
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 27,400
Tradenames, Customer Relationships and Technology
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	6,200	$ 5,900
Capitalized software development costs
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	500	$ 100
Advisory Services
Finite-Lived Intangible Assets [Line Items]
Goodwill	37,900
Technology Enabled Solutions
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 444,700