Intangible Assets - Summary Of Intangible Assets and Accumulated Amortization Included In The Consolidated Statements of Condition (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Intangible Assets [Line Items]
Gross Carrying Amount	$ 240,637	$ 240,637
Accumulated Amortization	(104,231)	(85,603)
Net Carrying Value	136,406	155,034
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	157,150	157,150
Accumulated Amortization	(42,566)	(28,150)
Net Carrying Value	114,584	129,000
Customer relationships
Intangible Assets [Line Items]
Gross Carrying Amount	77,865	77,865
Accumulated Amortization	(59,015)	(55,597)
Net Carrying Value	18,850	22,268
Other
Intangible Assets [Line Items]
Gross Carrying Amount	5,622	5,622
Accumulated Amortization	(2,650)	(1,856)
Net Carrying Value	2,972	3,766
State banking licenses
Intangible Assets [Line Items]
Indefinite-lived intangible assets, excluding goodwill	$ 300	$ 300