

	Carrying Amount
Balance as of December 31, 2017	$	128,728
Goodwill acquired	26,063
Foreign currency translation adjustments	(5,946		)
Balance as of December 31, 2018	148,845
Goodwill acquired	2,246
Foreign currency translation adjustments	5,665
Balance as of December 31, 2019	$	156,756



	December 31,			December 31,
	2019			2018
Developed technology	$	177,746		$	114,395
Patents	67,730			57,180
Other	3,594			650
Total intangible assets	249,070			172,225
Less: accumulated amortization	(105,220		)	(71,643		)
Net carrying amount	$	143,850		$	100,582

Apart from the business combinations described in Note 5, during the year ended December 31, 2019, we acquired $72.7 million in intangible assets, comprising primarily $61.0 million of developed technology and $10.6 million in patents. The weighted-average useful lives for the developed technology and patents acquired during the year ended December 31, 2019 was approximately five years and eight years, respectively. During the year end of December 31, 2018, we acquired $26.2 million of intangible assets in patents. The weighted-average useful life for patents acquired during the year ended December 31, 2018 was approximately seven years.

Amortization expense for intangible assets was approximately $34.6 million, $25.2 million, $19.7 million for the years ended December 31, 2019, 2018 and 2017, respectively.

The following table presents the estimated future amortization expense related to intangible assets held at December 31, 2019 (in thousands):



Years Ending December 31,
2020	$	35,641
2021	33,322
2022	28,343
2023	22,507
2024	15,809
Thereafter	8,228
Total future amortization expense	$	143,850