5.    Goodwill and Intangible Assets

There were no changes to the goodwill carrying value from December 31, 2020 through June 30, 2021. The foreign exchange impact on goodwill was immaterial for the period.

The following table summarizes the Company’s intangible assets and related accumulated amortization:

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Amortization expense for three months ended June 30, 2021 and June 30, 2020 is $4.4 million and $4.5 million, respectively. Amortization expense related to intangible assets amounted to $8.9 million and $9.0 million for the six months ended June 30, 2021 and June 30, 2020, respectively.

Estimated future expected amortization expense of intangible assets as of June 30, 2021, is as follows:

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The weighted-average remaining useful life by major asset classes as of June 30, 2021 is as follows:

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There were no impairments identified during the six months ended June 30, 2021 or June 30, 2020.