Goodwill and Other Intangible Assets - Current Year Amortization Expense for Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Total intangible amortization	$ 1,651	$ 1,563
Core Deposit Intangibles
Finite-Lived Intangible Assets [Line Items]
Total intangible amortization	1,618	1,530
Customer Relationship Intangible
Finite-Lived Intangible Assets [Line Items]
Total intangible amortization	$ 33	$ 33