Goodwill and Other Intangible Assets - Summary of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	$ 84,462	$ 84,462
Accumulated Amortization	(45,755)	(39,597)
Net Carrying Amount	38,707	44,865
Core deposit intangibles
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	82,492	82,492
Accumulated Amortization	(44,694)	(38,634)
Net Carrying Amount	37,798	43,858
Customer relationship intangible
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Amount	1,970	1,970
Accumulated Amortization	(1,061)	(963)
Net Carrying Amount	$ 909	$ 1,007