Intangible Assets - Summary Of Intangible Assets and Accumulated Amortization Included In The Consolidated Statements of Condition (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) branch	Dec. 31, 2017 USD ($)
Intangible Assets [Line Items]
Gross Carrying Amount	$ 240,637	$ 244,137
Accumulated Amortization	(79,142)	(59,748)
Net Carrying Value	$ 161,495	184,389
Number of branches divested | branch	2
State banking licenses
Intangible Assets [Line Items]
Net Carrying Value	$ 300
Core deposit intangibles
Intangible Assets [Line Items]
Gross Carrying Amount	157,150	160,650
Accumulated Amortization	(23,148)	(8,176)
Net Carrying Value	134,002	152,474
Customer relationships
Intangible Assets [Line Items]
Gross Carrying Amount	77,865	77,865
Accumulated Amortization	(54,404)	(50,777)
Net Carrying Value	23,461	27,088
Other
Intangible Assets [Line Items]
Gross Carrying Amount	5,622	5,622
Accumulated Amortization	(1,590)	(795)
Net Carrying Value	$ 4,032	$ 4,827