6.	Goodwill and Other Intangible Assets

Changes in the carrying amount of goodwill during the years ended December 31, 2017 and 2016 consisted of the following:


(dollars in millions)	North America		Rest of World			Total
Balance at December 31, 2015	$	361.0	$	59.9		$	420.9
Acquisitions		70.0		—			70.0
Currency translation adjustment		1.2		(0.6	)		0.6

Balance at December 31, 2016		432.2		59.3			491.5
Acquisitions		22.2		—			22.2
Currency translation adjustment		2.8		0.2			3.0

Balance at December 31, 2017	$	457.2	$	59.5		$	516.7

The carrying amount of other intangible assets consisted of the following:


	2017							2016
December 31 (dollars in millions)	Gross Carrying Amount		Accumulated Amortization			Net		Gross Carrying Amount		Accumulated Amortization			Net
Amortizable intangible assets:
Patents	$	3.7	$	(2.7	)	$	1.0	$	3.7	$	(2.2	)	$	1.5
Customer lists		235.8		(93.3	)		142.5		224.0		(80.3	)		143.7

Total amortizable intangible assets		239.5		(96.0	)		143.5		227.7		(82.5	)		145.2
Indefinite-lived intangible assets:
Trade names		165.2		—			165.2		163.1		—			163.1

Total intangible assets	$	404.7	$	(96.0	)	$	308.7	$	390.8	$	(82.5	)	$	308.3

Amortization expenses of other intangible assets of $13.7 million, $13.4 million, and $14.2 million were recorded in 2017, 2016 and 2015, respectively. In the future, excluding the impact of any future acquisitions, the Company expects amortization expense of approximately $14.5 million annually and the intangible assets will be amortized over a weighted average period of 12 years.

The Company concluded that no goodwill impairment existed at the time of the annual impairment tests which were performed in the fourth quarters of 2017, 2016 and 2015. No impairments of other intangible assets were recorded in 2017, 2016 and 2015.