Goodwill and Other Intangible Assets - Summary of Finite-lived Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 84,462	$ 56,928
Accumulated Amortization	(39,597)	(32,418)
Net Carrying Amount	44,865	24,510
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	82,492	54,958
Accumulated Amortization	(38,634)	(31,586)
Net Carrying Amount	43,858	23,372
Customer relationship intangible
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,970	1,970
Accumulated Amortization	(963)	(832)
Net Carrying Amount	$ 1,007	$ 1,138