Investment Securities - Narrative (Details) $ in Thousands	Jun. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Carrying value of securities pledged as collateral	$ 484,218	$ 475,999
Book value of securities sold under agreements to repurchase	125,412	136,639
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Held-to-maturity unrealized losses	6,415	$ 2,083
State and municipal
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Available-for-sale unrealized losses	$ 7,419
Available-for-sale, number of securities in unrealized loss positions | security	223
Held-to-maturity unrealized losses	$ 955
Held-to-maturity, number of securities in unrealized loss positions | security	48
U.S. Government-sponsored agency securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Available-for-sale unrealized losses	$ 23
Available-for-sale, number of securities in unrealized loss positions | security	5
Held-to-maturity unrealized losses	$ 755
Held-to-maturity, number of securities in unrealized loss positions | security	5
U.S. Government-sponsored mortgage-backed securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Available-for-sale unrealized losses	$ 12,984
Available-for-sale, number of securities in unrealized loss positions | security	114
Held-to-maturity unrealized losses	$ 4,699
Held-to-maturity, number of securities in unrealized loss positions | security	80