The changes in the carrying amount of goodwill for the fiscal years ended December 31 were as follows:

	2021			2020
Balance as of January 1	$	909,913		$	719,934
Goodwill resulting from business combination - ITG		—			188,253
Goodwill resulting from business combination - ESAC		11,226			—
Goodwill resulting from business combination - Creative Systems and Consulting		126,118			—
Effect of foreign currency translation		(497	)		1,726
Balance as of December 31	$	1,046,760		$	909,913

Intangible assets with definite lives are primarily amortized over periods ranging from approximately 1 to 10 years. The weighted-average period of amortization for all intangible assets, calculated as of December 31, 2021, is 7.7 years. The customer-related intangible assets, which consist of customer contracts, backlog, and non-contractual customer relationships, are being amortized based on estimated cash flows and respective estimated economic benefit of the assets. The weighted-average period of amortization of the customer-related intangibles calculated as of December 31, 2021 is 7.7 years. Intangible assets related to developed technology are being amortized on an accelerated basis over a weighted-average period, calculated as of December 31, 2021, of 7.7 years. Intangible assets with an indefinite life consist of a domain name.

	2021
	Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Customer-related	$	167,577	$	(92,494	)	$	75,083
Developed technology		5,411		(944	)		4,467
Total amortizable intangible assets		172,988		(93,438	)		79,550
Intangible with indefinite life		95		—			95
Total other intangible assets	$	173,083	$	(93,438	)	$	79,645

	2020
	Gross Carrying Value		Accumulated Amortization			Net Carrying Value
Customer-related	$	142,849	$	(83,137	)	$	59,712
Developed technology		733		(653	)		80
Total amortizable intangible assets		143,582		(83,790	)		59,792
Intangible with indefinite life		95		—			95
Total other intangible assets	$	143,677	$	(83,790	)	$	59,887

Aggregate amortization expense for the years ended December 31, 2021, 2020, and 2019, was approximately $12.5 million, $13.3 million, and $8.1 million, respectively. The Company recognized impairment expense, included in indirect and selling expense, of $1.7 million in the second quarter of 2019 related to the intangible asset associated with a historical business acquisition. The estimated future amortization expense relating to intangible assets is as follows:

Year ending December 31,
2022	$	19,920
2023		18,864
2024		18,211
2025		13,393
2026		7,207
Thereafter		1,955
Total	$	79,550