The table below reconciles the change in the carrying amount of goodwill for the period from January 1, 2020 to June 30, 2020:

	GRE		GRE International			GES	Total
	(in thousands)
Balance at January 1, 2020	$	9,998	$	1,733	$	404	$	12,135
Cumulative translation adjustment		—		2		—		2
Balance at June 30, 2020	$	9,998	$	1,735	$	404	$	12,137

The table below presents information on the Company’s other intangible assets:

	Weighted Average Amortization Period		Gross Carrying Amount		Accumulated Amortization		Net Balance
	(in thousands)
June 30, 2020
Patents and trademarks		17.1 years	$	3,842	$	695	$	3,147
Non-compete agreements		3.0 years		34		17		17
Customer relationships		4.6 years		3,009		1,777		1,232
Licenses		10.0 years		1,224		180		1,044
Total			$	8,109	$	2,669	$	5,440
December 31, 2019
Trademark		17.1 years	$	3,842	$	560	$	3,282
Non-compete agreement		1.6 years		148		126		22
Customer relationships		3.9 years		6,706		3,941		2,765
Licenses		10.0 years		895		127		768
Total			$	11,591	$	4,754	$	6,837

In the second quarter of 2020, Prism renegotiated a contract with its main customer which resulted in impairment of customer relationship of $0.8 million included in the consolidated statements of operations.

Amortization expense of intangible assets (including minimal amounts reported in cost of revenues) was $0.4 million and $0.9 million in the three and six months ended June 30, 2020, respectively. Amortization expense of intangible assets (including minimal amounts reported in cost of revenues) was $0.5 million and $1.0 million in the three and six months ended June 30, 2019, respectively. The Company estimates that amortization expense of intangible assets will be $0.7 million, $0.5 million, $0.5 million, $0.5 million, $0.5 million and $2.7 million for the remainder of 2020, and for 2021, 2022, 2023, 2024 and thereafter, respectively.