The following table summarizes the carrying amount of goodwill, and the changes in the carrying amount of goodwill in the six months ended June 30, 2025, by segment:


(in millions)	Environmental Solutions		Safety & Security Systems		Total
Balance at January 1, 2025	$	368.8	$	108.9	$	477.7
Acquisitions, including measurement period adjustments	35.2		—		35.2
Translation adjustments	0.6		4.1		4.7
Balance at June 30, 2025	$	404.6	$	113.0	$	517.6

The following table summarizes the gross carrying amount and accumulated amortization of intangible assets for each major class of intangible assets:


	June 30, 2025						December 31, 2024
(in millions)	Gross Carrying Value		Accumulated Amortization		Net Carrying Value		Gross Carrying Value		Accumulated Amortization		Net Carrying Value
Definite-lived intangible assets:
Customer relationships (a)	$	182.8	$	(89.0)	$	93.8	$	165.7	$	(80.7)	$	85.0
Other (a)	10.8		(5.6)		5.2		7.2		(4.9)		2.3
Total definite-lived intangible assets	193.6		(94.6)		99.0		172.9		(85.6)		87.3
Indefinite-lived intangible assets:
Trade names	119.2		—		119.2		108.1		—		108.1
Other	4.3		—		4.3		4.3		—		4.3
Total indefinite-lived intangible assets	123.5		—		123.5		112.4		—		112.4
Total intangible assets	$	317.1	$	(94.6)	$	222.5	$	285.3	$	(85.6)	$	199.7

(a) Average useful life of customer relationships and other definite-lived intangible assets are estimated to be approximately 11 years and 6 years, respectively. The average useful life across all definite-lived intangible assets is estimated to be approximately 11 years.

The table above includes preliminary estimates of the fair value and useful lives of certain definite and indefinite-lived intangible assets related to the acquisitions of Hog, which was acquired during the first quarter of 2025, and Standard Equipment Company (“Standard”), which was acquired during the fourth quarter of 2024. As further described in Note 2 – Acquisitions, the preliminary measurements of fair value included in the table above are subject to change during the measurement period as the applicable third-party valuations are finalized.

Amortization expense was $4.5 million for the three months ended June 30, 2025 and $8.8 million for the six months ended June 30, 2025. Amortization expense was $3.8 million for the three months ended June 30, 2024 and $7.4 million for the six months ended June 30, 2024.

The Company currently estimates that aggregate amortization expense will be approximately $9.0 million for the remainder of 2025, $17.9 million in 2026, $17.0 million in 2027, $16.7 million in 2028, $11.0 million in 2029, and $27.4 million thereafter. Actual amounts of amortization may differ from estimated amounts due to changes in foreign currency rates, measurement period adjustments for the Hog and Standard acquisitions, impairment of intangible assets, and other events.