Goodwill and Other Intangible Assets - Summary Of Intangible Assets and Accumulated Amortization Included In The Consolidated Statements of Condition (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Intangible Assets [Line Items]
Gross Carrying Amount	$ 446,535	$ 240,637
Accumulated Amortization	(80,835)	(110,437)
Intangible Assets, Net (Excluding Goodwill), Total	365,700	130,200
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	370,850	157,150
Accumulated Amortization	(68,902)	(47,372)
Intangible Assets, Net (Excluding Goodwill), Total	301,948	109,778
Customer relationships
Intangible Assets [Line Items]
Gross Carrying Amount	37,000	77,865
Accumulated Amortization	(7,037)	(60,150)
Intangible Assets, Net (Excluding Goodwill), Total	29,963	17,715
Other
Intangible Assets [Line Items]
Gross Carrying Amount	38,685	5,622
Accumulated Amortization	(4,896)	(2,915)
Intangible Assets, Net (Excluding Goodwill), Total	$ 33,789	$ 2,707