Investment Securities - Contractual Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Due in 1 year or less, Securities available for sale, Amortized Cost	$ 0	$ 111	$ 176
Due in 1 to 5 years, Securities available for sale, Amortized Cost	13,961	841	856
Due in 5 to 10 years, Securities available for sale, Amortized Cost	69,317	29,003	33,550
Due after 10 years, Securities available for sale, Amortized Cost	230,470	270,594	262,429
Equity securities, Amortized Cost	3,257	3,296	3,257
Amortized Cost	317,005
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Due in 1 year or less, Securities available for sale, Fair Value (Estimated)	0	112	179
Due in 1 to 5 years, Securities available for sale, Fair Value (Estimated)	13,886	842	859
Due in 5 to 10 years, Securities available for sale, Fair Value (Estimated)	67,434	29,177	33,987
Due after 10 years, Securities available for sale, Fair Value (Estimated)	220,867	266,627	260,606
Other equity securities	3,257	3,414	3,368
Securities available for sale, Fair Value (Estimated)	305,444
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Due in 1 year or less, Securities to be held to maturity, Amortized Cost	1,796	635	552
Due in 1 to 5 years, Securities to be held to maturity, Amortized Cost	21,463	18,059	17,241
Due in 5 to 10 years, Securities to be held to maturity, Amortized Cost	155,997	37,182	37,218
Due after 10 years, Securities to be held to maturity, Amortized Cost	78,139	200,691	187,668
Securities to be held to maturity, Amortized Cost	257,395	256,567	242,679
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Due in 1 year or less, Securities to be held to maturity, Fair Value (Estimated)	1,800	637	559
Due in 1 to 5 years, Securities to be held to maturity, Fair Value (Estimated)	21,468	18,164	17,485
Due in 5 to 10 years, Securities to be held to maturity, Fair Value (Estimated)	152,154	37,719	37,963
Due after 10 years, Securities to be held to maturity, Fair Value (Estimated)	74,468	203,135	189,014
Securities to be held to maturity, Fair Value (Estimated)	$ 249,890	$ 259,655	$ 245,021

Debt Securities, Available-for-sale, Amortized Cost and Equity Securities

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