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Investment Securities - Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	$ 164,222	$ 151,032
Held to maturity, Fair Value	158,106	151,032
Held-to-maturity, Gross Unrealized Gains	160	619
Held-to-maturity, Gross Unrealized Losses	(6,276)	(619)
Total	416,732	334,285
Available-for-sale, at fair value	405,571	332,467
Available-for-sale, Gross Unrealized Gains	88	574
Available-for-sale, Gross Unrealized Losses	(11,249)	(2,392)
Total investment securities, Amortized Cost	580,954	485,317
Total investment securities, Fair Value	563,677	483,499
Total investment securities, Gross Unrealized Gains	248	1,193
Total investment securities, Gross Unrealized Losses	(17,525)	(3,011)
MBS pass-through securities issued by FHLMC and FNMA
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	91,237	100,376
Held to maturity, Fair Value	86,962	100,096
Held-to-maturity, Gross Unrealized Gains	0	234
Held-to-maturity, Gross Unrealized Losses	(4,275)	(514)
Total	93,096	65,559
Available-for-sale, at fair value	90,484	65,262
Available-for-sale, Gross Unrealized Gains	20	126
Available-for-sale, Gross Unrealized Losses	(2,632)	(423)
SBA-backed securities
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	8,723	0
Held to maturity, Fair Value	8,489	0
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized Losses	(234)	0
Total	41,074	25,979
Available-for-sale, at fair value	40,181	25,982
Available-for-sale, Gross Unrealized Gains	0	58
Available-for-sale, Gross Unrealized Losses	(893)	(55)
CMOs issued by FNMA
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	11,646	0
Held to maturity, Fair Value	11,254	0
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized Losses	(392)	0
Total	19,914	35,340
Available-for-sale, at fair value	19,356	35,125
Available-for-sale, Gross Unrealized Gains	4	33
Available-for-sale, Gross Unrealized Losses	(562)	(248)
CMOs issued by FHLMC
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	34,169	31,010
Held to maturity, Fair Value	32,868	30,938
Held-to-maturity, Gross Unrealized Gains	0	2
Held-to-maturity, Gross Unrealized Losses	(1,301)	(74)
Total	128,848	70,514
Available-for-sale, at fair value	124,930	69,889
Available-for-sale, Gross Unrealized Gains	1	3
Available-for-sale, Gross Unrealized Losses	(3,919)	(628)
CMOs issued by GNMA
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	3,734	0
Held to maturity, Fair Value	3,694	0
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Gross Unrealized Losses	(40)	0
Total	11,938	17,953
Available-for-sale, at fair value	11,450	17,785
Available-for-sale, Gross Unrealized Gains	0	26
Available-for-sale, Gross Unrealized Losses	(488)	(194)
Debentures of government- sponsored agencies
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Total	43,470	12,940
Available-for-sale, at fair value	42,914	12,938
Available-for-sale, Gross Unrealized Gains	0	3
Available-for-sale, Gross Unrealized Losses	(556)	(5)
Privately issued CMOs
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Total	367	1,432
Available-for-sale, at fair value	370	1,431
Available-for-sale, Gross Unrealized Gains	3	1
Available-for-sale, Gross Unrealized Losses	0	(2)
Obligations of state and political subdivisions
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Held to maturity, Amortized Cost	14,713	19,646
Held to maturity, Fair Value	14,839	19,998
Held-to-maturity, Gross Unrealized Gains	160	383
Held-to-maturity, Gross Unrealized Losses	(34)	(31)
Total	75,519	98,027
Available-for-sale, at fair value	73,373	97,491
Available-for-sale, Gross Unrealized Gains	41	298
Available-for-sale, Gross Unrealized Losses	(2,187)	(834)
Corporate bonds
Schedule of Available-for-sale Securities and Held-to-maturity Securities [Line Items]
Total	2,506	6,541
Available-for-sale, at fair value	2,513	6,564
Available-for-sale, Gross Unrealized Gains	19	26
Available-for-sale, Gross Unrealized Losses	$ (12)	$ (3)

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