Goodwill and Other Intangible Assets - Summary of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 84,462	$ 84,462
Accumulated Amortization	(41,707)	(39,597)
Net Carrying Amount	42,755	44,865
Core Deposit Intangibles
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	82,492	82,492
Accumulated Amortization	(40,711)	(38,634)
Net Carrying Amount	41,781	43,858
Customer Relationship Intangible
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	1,970	1,970
Accumulated Amortization	(996)	(963)
Net Carrying Amount	$ 974	$ 1,007