NOTE 8—INTANGIBLE ASSETS

The carrying amount of intangible assets, net of accumulated amortization and impairment charges, as of December 31, 2019 and 2018 consisted of the following:


			2019
			Gross
	Estimated		Carrying		Accumulated		Currency		Net Book
	Useful Lives		Amount		Amortization		impact		Value
Amortizable intangibles:
Customer relationships	2 to 15	years	$	73,723	$	(63,761)	$	(116)	$	9,846
Noncompete agreements	4 to 7	years		5,952		(5,862)		1		91
Software	3 to 4	years		1,500		(1,500)		—		—
Backlog	1 to 2	years		5,002		(4,981)		(21)		—
Databases	4 to 15	years		13,218		(6,364)		(186)		6,668
Trademark and trade names	5	years		1,250		(1,250)		—		—
Intangibles			$	100,645	$	(83,718)	$	(322)	$	16,605


			2018
			Gross
	Estimated		Carrying		Accumulated		Currency		Net Book
	Useful Lives		Amount		Amortization		impact		Value
Amortizable intangibles:
Customer relationships	2 to 15	years	$	73,723	$	(60,256)	$	(112)	$	13,355
Noncompete agreements	4 to 7	years		5,952		(5,812)		1		141
Software	3 to 4	years		1,500		(1,500)		—		—
Backlog	1 to 2	years		5,002		(4,981)		(21)		—
Databases	4 to 15	years		13,218		(5,908)		(184)		7,126
Trademark and trade names	5	years		1,250		(1,250)		—		—
Intangibles			$	100,645	$	(79,707)	$	(316)	$	20,622

Amortization expense was $4.0 million and $5.0 million for the years ended December 31, 2019 and 2018, respectively. The estimated future amortization expense subsequent to December 31, 2019, is as follows:


2020	$	3,418
2021		2,062
2022		1,673
2023		1,421
2024		1,193
Thereafter		6,838
	$	16,605