5. Goodwill and intangible assets

Goodwill and intangible assets consisted of:



	December 31, 2020									December 31, 2019
(in thousands)	Useful life (months)		Gross carrying amount		Accumulated amortization			Net carrying amount		Gross carrying amount		Accumulated amortization			Net carrying amount
Technology and intellectual property		60	$	—	$	—		$	—	$	32,027	$	(32,027	)	$	—
Customer relationships		120		25,040		(10,016	)		15,024		25,040		(7,094	)		17,946
Costs to acquire third party publishers		24		—		—			—		1,363		(1,363	)		—
Non-compete agreements		60		303		(211	)		92		303		(155	)		148
Domain names		60		1,224		(789	)		435		1,224		(566	)		658

Intangible assets			$	26,567	$	(11,016	)	$	15,551	$	59,957	$	(41,205	)	$	18,752
Goodwill		Indefinite	$	18,402		—		$	18,402	$	18,402		—		$	18,402

Amortization expense related to intangible assets amounted to $3.2 million, $5.4 million, and $11.8 million for the years ended December 31, 2020, 2019, and 2018, respectively. We did not have any impairments of goodwill for the years ended December 31 2020 and 2019, respectively.

The following table presents the change in goodwill and intangible assets:



	December 31, 2020					December 31, 2019
(in thousands)	Goodwill		Intangible assets			Goodwill		Intangible assets
Beginning balance at January 1,	$	18,402	$	18,752		$	18,402	$	23,985
Addition to goodwill and intangible assets		—		—			—		148
Amortization		—		(3,201	)		—		(5,381	)

Ending balance	$	18,402	$	15,551		$	18,402	$	18,752

As of December 31, 2020, future amortization expense on identifiable intangible assets with estimable useful lives over the next five years is as follows:



(in thousands)	Amortization expense
2021	$	2,983
2022		2,730
2023		2,388
2024		2,211
2025		2,028
Thereafter		3,211

	$	15,551