4.   Intangible Assets

We evaluate goodwill and tradenames for impairment annually or more frequently when an event occurs or circumstances change that indicates the carrying value of a reporting unit may not be recoverable. In March 2020, the Company announced a voluntary suspension of all cruise voyages for its three brands, which has subsequently been extended through October 31, 2020. Due to the temporary suspension of operations and decline in our stock price, we performed interim goodwill and tradename impairment tests as of March 31, 2020. We refer you to Note 9 – “Fair Value Measurements and Derivatives” for information on our valuation assumptions.

The changes in the carrying amount of goodwill for each reporting unit for the six months ended June 30, 2020 are as follows (in thousands):

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We also impaired our tradenames for Oceania Cruises and Regent Seven Seas Cruises by $170.0 million and $147.0 million, respectively. Following these impairments, the carrying value of our tradenames was $500.5 million.

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The carrying amounts of intangible assets subject to amortization are included within other long-term assets. The gross carrying amounts of intangible assets, the related accumulated amortization, the net carrying amounts and the weighted-average amortization periods of the Company’s intangible assets are listed in the following tables (in thousands, except amortization period):

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The aggregate amortization expense for intangible assets is as follows (in thousands):

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The following table sets forth the Company’s estimated aggregate amortization expense for each of the five years below (in thousands):

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