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Goodwill and Other Intangible Assets - Textual (Details) - USD ($)	3 Months Ended					12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 1,075,305,000	$ 1,075,305,000				$ 1,075,305,000
Goodwill impairment		$ 0	$ 0	$ 0	$ 0	$ 0
Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	15 years
Core Deposit Premium | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life	10 years
Core Deposit Premium | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life	15 years

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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