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Other Intangibles
 3 Months Ended
Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]  
Other Intangibles
OTHER INTANGIBLES

Core deposit intangibles are recorded on the acquisition date of an entity. The carrying basis and accumulated amortization of recognized core deposit intangibles are noted below.

March 31, 2021December 31, 2020
Gross carrying amount$102,396 $102,396 
Accumulated amortization(74,778)(73,421)
Total core deposit intangibles$27,618 $28,975 
The core deposit intangibles are being amortized primarily on an accelerated basis over their estimated useful lives, generally over a period of ten years. Intangible asset amortization expense for the three months ended March 31, 2021 was $1.4 million compared to $1.5 million for the three months ended March 31, 2020. Estimated future amortization expense is summarized as follows:
Amortization Expense
2021$4,072 
20225,027 
20234,827 
20244,241 
20253,526 
After 20255,925 
$27,618