The following table summarizes the changes in the carrying amount of goodwill (in millions):


	Amount
Balance as of December 31, 2023	$	348.7
Acquisition activity	—
Translation and other	(0.7)
Balance as of June 30, 2024	$	348.0

The following table summarizes the components of gross intangible assets, accumulated amortization, and net intangible assets balances as of June 30, 2024, and December 31, 2023 (in millions):


	June 30, 2024						December 31, 2023
	Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount
Patents and developed technology	$	206.3	$	(185.3)	$	21.0	$	206.3	$	(178.4)	$	27.9
Distribution rights and others	10.7		(10.1)		0.6		10.8		(9.2)		1.6
Customer relationships	27.5		(20.4)		7.1		32.5		(22.9)		9.6
Total intangible assets	$	244.5	$	(215.8)	$	28.7	$	249.6	$	(210.5)	$	39.1

Amortization expense related to intangible assets was $5.0 million and $5.0 million for the three months ended June 30, 2024, and 2023, respectively. Amortization expense related to intangible assets was $10.1 million and $10.0 million for the six months ended June 30, 2024, and 2023, respectively.

The estimated future amortization expense related to intangible assets as of June 30, 2024, is as follows (in millions):


Fiscal Year	Amount
Remainder of 2024	$	6.8
2025	11.9
2026	5.2
2027	2.8
2028	1.3
2029 and thereafter	0.7
Total	$	28.7

The preceding expected amortization expense is an estimate. Actual amounts of amortization expense may differ from estimated amounts due to additional intangible asset acquisitions, measurement-period adjustments to intangible assets, changes in foreign currency exchange rates, impairments of intangible assets, accelerated amortization of intangible assets, and other events.