Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 67,131	$ 73,749
Gross Unrealized Gains	6	85
Gross Unrealized Losses	(2,721)	(376)
Fair Value	64,416	73,458
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	691,989	647,141
Gross Unrealized Gains	418	1,407
Gross Unrealized Losses	(22,079)	(7,166)
Fair Value	670,328	641,382
US Treasury Bill Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,960
Gross Unrealized Gains	0
Gross Unrealized Losses	(193)
Fair Value	9,767
Obligations of U.S. Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,914	99,878
Gross Unrealized Gains	0	6
Gross Unrealized Losses	(2,233)	(660)
Fair Value	97,681	99,224
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,563	34,181
Gross Unrealized Gains	238	674
Gross Unrealized Losses	(268)	(213)
Fair Value	30,533	34,642
Agency mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	551,552	513,082
Gross Unrealized Gains	180	727
Gross Unrealized Losses	(19,385)	(6,293)
Fair Value	532,347	507,516
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,521	14,031
Gross Unrealized Gains	6	69
Gross Unrealized Losses	(324)	(46)
Fair Value	12,203	14,054
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	54,610	59,718
Gross Unrealized Gains	0	16
Gross Unrealized Losses	(2,397)	(330)
Fair Value	$ 52,213	$ 59,404

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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