Goodwill and Other Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Amortizable intangible assets:
Intangible asset - net	$ 21,425		$ 23,076
Amortization expense	1,651	$ 1,447
Estimated amortization expense
For the year ending December 31, 2020	6,237
For the year ending December 31, 2021	5,058
For the year ending December 31, 2022	3,976
For the year ending December 31, 2023	3,016
For the year ending December 31, 2024	2,249
For the year ending December 31, 2025	1,510
Core Deposits
Amortizable intangible assets:
Intangible asset - gross	71,183		71,183
Less: accumulated amortization	(52,357)		(50,934)
Intangible asset - net	18,826		20,249
Customer and Contract
Amortizable intangible assets:
Intangible asset - gross	12,775		12,775
Less: accumulated amortization	(10,176)		(9,948)
Intangible asset - net	$ 2,599		$ 2,827

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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