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Basis of Presentation (Details) $ in Thousands		3 Months Ended
	Jan. 01, 2020 USD ($)	Mar. 31, 2021 USD ($) subsidiary segment	Dec. 31, 2020 USD ($)
Basis of presentation
Number of operating segments | segment		1
Number of active operating bank subsidiaries | subsidiary		5
Retained earnings		$ 2,305,584	$ 2,289,626
ASU 2016-13 | Adjustment
Basis of presentation
Percentage of allowance for loan losses	17.20%
Retained earnings	$ 8,300

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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