Investment Securities - Narrative (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($) security	Dec. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
AFS and HTM securities in unrealized loss positions qualitative disclosure number of positions | security	124
Unrealized losses as a percentage of individual securities amortized cost basis	3.50%
Unrealized losses as percentage of Company's total amortized cost basis	2.94%
Number of securities in an unrealized loss position for over 12 months | security	60
Amortized cost basis of securities in a continuous loss position	$ 223,200,000
Unrealized loss on securities in a continuous loss position	10,900,000
Impairment related to credit quality	$ 0
Number of securities sold | security	1	16
Proceeds from sale of securities available-for-sale	$ 410,000
Number of held to maturity securities sold | security		1
Available-for-sale securities, realized gain (loss)		$ 340,000
Held-to-maturity security gain		$ 7,000
Accelerated maturity period		15 years
Anticipated call period		6 months
Number of available-for-sale securities sold with gains | security		13
Available-for-sale securities, gross realized gains		$ 449,000
Number of available-for-sale securities sold with losses | security		3
Available-for-sale securities, gross realized losses		$ 109,000
Securities pledged as collateral for public funding	$ 189,400,000		$ 189,000,000