(9) Goodwill and Intangibles

For acquired businesses, we record assets acquired and liabilities assumed at their estimated fair values on the respective acquisition dates. Based on these values, the excess purchase prices over the fair value of the net assets acquired is recorded as goodwill. Of the $706.8 million total goodwill at September 30, 2018, $468.7 million related to the North America Storage Solutions segment, $56.9 million related to the U.K. Storage Solutions segment and $181.2 million related to the Tank & Pump Solutions segment.

The following table shows the activity and balances related to goodwill from January 1, 2018 to September 30, 2018 (in thousands):

Balance at January 1, 2018	$	708,907
Foreign currency		(2,139	)
Balance at September 30, 2018	$	706,768

Intangible assets are amortized over the estimated useful life of the asset utilizing a method which reflects the estimated pattern in which the economic benefits will be consumed. Customer relationships are amortized based on the estimated attrition rates of the underlying customer base. Other intangibles are amortized using the straight-line method.

The following table reflects balances related to intangible assets for the periods presented:

		September 30, 2018							December 31, 2017
	Estimated Useful Life in Years	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
		(In thousands)
Customer relationships	15 - 20	$	92,946	$	(38,342	)	$	54,604	$	93,235	$	(34,660	)	$	58,575
Trade names/trademarks	5 - 10		5,929		(3,826	)		2,103		5,954		(3,312	)		2,642
Non-compete agreements	5		1,888		(1,459	)		429		1,890		(1,114	)		776
Other	20		59		(31	)		28		60		(29	)		31
Total		$	100,822	$	(43,658	)	$	57,164	$	101,139	$	(39,115	)	$	62,024

Amortization expense for amortizable intangibles was approximately $4.8 million and $4.9 million for the nine-month periods ended September 30, 2018 and 2017, respectively. Based on the carrying value at September 30, 2018, future amortization of intangible assets is expected to be as follows for the years ended December 31 (in thousands):

2018 (remaining)	$	1,603
2019		6,304
2020		5,143
2021		4,907
2022		4,606
Thereafter		34,601
Total	$	57,164