Investment Securities - Narrative (Details) $ in Thousands	Mar. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Carrying value of securities pledged as collateral	$ 552,899	$ 475,999
Book value of securities sold under agreements to repurchase	141,664	136,639
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Held-to-maturity unrealized losses	5,394	$ 2,083
State and municipal
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Available-for-sale unrealized losses	$ 7,238
Available-for-sale, number of securities in unrealized loss positions | security	208
Held-to-maturity unrealized losses	$ 911
Held-to-maturity, number of securities in unrealized loss positions | security	46
U.S. Government-sponsored agency securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Available-for-sale unrealized losses	$ 1
Available-for-sale, number of securities in unrealized loss positions | security	1
Held-to-maturity unrealized losses	$ 715
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	$ 10,039
Available-for-sale, number of securities in unrealized loss positions | security	101
Held-to-maturity unrealized losses	$ 3,762
Held-to-maturity, number of securities in unrealized loss positions | security	76