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Other Intangibles
 12 Months Ended
Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]  
Other Intangibles
OTHER INTANGIBLES

Core deposit intangibles and other intangibles are recorded on the acquisition date of an entity. During the one-year measurement period, the Corporation may record subsequent adjustments to these intangibles for provisional amounts recorded at the acquisition date. The MBT acquisition on September 1, 2019 resulted in a core deposit intangible of $16,527,000. Details regarding the MBT acquisition are discussed in NOTE 2. ACQUISITION of these Notes to Consolidated Financial Statements.

The carrying basis and accumulated amortization of recognized core deposit and other intangibles are noted below.
 20202019
Gross carrying amount$102,396 $85,869 
Core deposit intangible acquired— 16,527 
Accumulated amortization(73,421)(67,434)
Total core deposit and other intangibles$28,975 $34,962 
 

The core deposit intangibles and other intangibles are being amortized primarily on an accelerated basis over their estimated useful lives, generally over a period of two to ten years. Amortization expense for the years ended December 31, 2020, 2019 and 2018, was $5,987,000, $5,994,000 and $6,719,000, respectively.
Estimated future amortization expense is summarized as follows:
Amortization Expense
2021$5,429 
20225,027 
20234,827 
20244,241 
20253,526 
After 20255,925 
 $28,975