Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 68,931	$ 73,749
Gross Unrealized Gains	7	85
Gross Unrealized Losses	(2,029)	(376)
Fair Value	66,909	73,458
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	667,419	647,141
Gross Unrealized Gains	717	1,407
Gross Unrealized Losses	(16,996)	(7,166)
Fair Value	651,140	641,382
US Treasury Bill Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,957
Gross Unrealized Gains	0
Gross Unrealized Losses	(94)
Fair Value	9,863
Obligations of U.S. Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,902	99,878
Gross Unrealized Gains	0	6
Gross Unrealized Losses	(1,858)	(660)
Fair Value	98,044	99,224
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31,750	34,181
Gross Unrealized Gains	348	674
Gross Unrealized Losses	(154)	(213)
Fair Value	31,944	34,642
Agency mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	525,810	513,082
Gross Unrealized Gains	369	727
Gross Unrealized Losses	(14,890)	(6,293)
Fair Value	511,289	507,516
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,537	14,031
Gross Unrealized Gains	7	69
Gross Unrealized Losses	(240)	(46)
Fair Value	12,304	14,054
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	56,394	59,718
Gross Unrealized Gains	0	16
Gross Unrealized Losses	(1,789)	(330)
Fair Value	$ 54,605	$ 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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