GOODWILL AND OTHER INTANGIBLE ASSETS

The following table presents the changes in the carrying amount of goodwill and other intangible assets during the year ended December 31, 2018 (in thousands):



	Goodwill		Other Intangible Assets			Total
Balances as of December 31, 2017	$	187,591	$	78,525		$	266,116
Translation adjustment	—		(917		)	(917		)
Acquisition of ASI	6,461		6,185			12,646
Amortization	—		(16,586		)	(16,586		)
Balances as of December 31, 2018	$	194,052	$	67,207		$	261,259

The following table presents the changes in the carrying amount of goodwill and other intangible assets during the year ended December 31, 2017 (in thousands):



	Goodwill		Other Intangible Assets			Total
Balances as of December 31, 2016	$	187,591	$	94,831		$	282,422
Translation adjustment	—		960			960
Amortization	—		(17,266		)	(17,266		)
Balances as of December 31, 2017	$	187,591	$	78,525		$	266,116

The following table presents the goodwill balance by reportable segment as of December 31, 2018 and 2017 (in thousands):



	As of December 31,
	2018		2017
Service Centers	$	160,934	$	154,473
Innovative Pumping Solutions	15,980		15,980
Supply Chain Services	17,138		17,138
Total	$	194,052	$	187,591

The following table presents a summary of amortization of other intangible assets ( in thousands):



	As of December 31, 2018							As of December 31, 2017
	Gross Carrying Amount		Accumulated Amortization			Carrying Amount, net		Gross Carrying Amount		Accumulated Amortization			Carrying Amount, net
Customer relationships	$	168,255	$	(101,200	)	$	67,055	$	162,200	$	(83,806	)	$	78,394
Non-compete agreements	784		(632		)	152		949		(818		)	131
Total	$	169,039	$	(101,832	)	$	67,207	$	163,149	$	(84,624	)	$	78,525

Gross carrying amounts as well as accumulated amortization are partially affected by the fluctuation of foreign currency rates. Other intangible assets are amortized according to estimated economic benefits over their estimated useful lives.

Customer relationships are amortized over their estimated useful lives. Amortization expense is recognized according to estimated economic benefits and was $16.6 million, $17.3 million, and $18.1 million for the years ended December 31, 2018, 2017, and 2016, respectively. The estimated future annual amortization of intangible assets for each of the next five years and thereafter are as follows (in thousands):



2019	$	15,479
2020	12,674
2021	10,792
2022	10,091
2023	8,665
Thereafter	9,506
Total	$	67,207

The weighted average remaining estimated life for customer relationships and non-compete agreements are 5.5 years and 3.2 years, respectively.