Goodwill and Other Intangible Assets - Summary of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 56,928	$ 56,928
Accumulated Amortization	(34,069)	(32,418)
Net Carrying Amount	22,859	24,510
Core Deposit Intangibles
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	54,958	54,958
Accumulated Amortization	(33,204)	(31,586)
Net Carrying Amount	21,754	23,372
Customer Relationship Intangible
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	1,970	1,970
Accumulated Amortization	(865)	(832)
Net Carrying Amount	$ 1,105	$ 1,138