Goodwill and Other Intangible Assets - Summary of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 84,282	$ 56,928
Accumulated Amortization	(37,428)	(32,418)
Net Carrying Amount	46,854	24,510
Core Deposit Intangibles
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	82,312	54,958
Accumulated Amortization	(36,497)	(31,586)
Net Carrying Amount	45,815	23,372
Customer Relationship Intangible
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	1,970	1,970
Accumulated Amortization	(931)	(832)
Net Carrying Amount	$ 1,039	$ 1,138