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Intangible assets
 6 Months Ended
Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]  
Intangible assets Intangible assets
The carrying amount of Intangible Assets for the periods ended June 30, 2024 and December 31, 2023 is as follows:

June 30,
2024		December 31,
2023
(in thousands)
Cost
Customer relationships$4,089,261 $4,090,393 
Order backlog540,795 541,302 
Trade names & brands204,621 204,653 
Patient database170,348 170,366 
Technology assets150,933 141,257 
Total cost5,155,958 5,147,971 
Accumulated amortization(1,523,604)(1,292,106)
 Net book value$3,632,354 $3,855,865 

In the six months ended June 30, 2024, the amortization expense recognized by the Company was $233.0 million (year ended December 31, 2023: $459.9 million).

On January 9, 2024, the Company acquired HumanFirst. The acquisition resulted in the recognition of a developed technology intangible asset of $9.9 million. Refer to note 5. Goodwill for further details.
The identifiable intangible assets are amortized over their estimated useful lives.