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Goodwill and Core Deposit Intangibles - Goodwill Narrative (Details) - USD ($)
3 Months Ended 12 Months Ended
Jul. 01, 2019
Jul. 01, 2017
Jul. 01, 2015
Dec. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Goodwill [Line Items]              
Finite-Lived Intangible Asset, Useful Life         10 years    
Change in goodwill       $ 100,000      
Goodwill       $ 621,600,000 $ 621,600,000 $ 546,700,000 $ 444,700,000
Impairment of goodwill $ 0 $ 0 $ 0