Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 70,579	$ 73,749
Gross Unrealized Gains	7	85
Gross Unrealized Losses	(1,820)	(376)
Fair Value	68,766	73,458
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	667,194	647,141
Gross Unrealized Gains	746	1,407
Gross Unrealized Losses	(15,668)	(7,166)
Fair Value	652,272	641,382
US Treasury Bill Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,955
Gross Unrealized Gains	0
Gross Unrealized Losses	(48)
Fair Value	9,907
Obligations of U.S. Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,890	99,878
Gross Unrealized Gains	0	6
Gross Unrealized Losses	(1,698)	(660)
Fair Value	98,192	99,224
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,611	34,181
Gross Unrealized Gains	386	674
Gross Unrealized Losses	(209)	(213)
Fair Value	32,788	34,642
Agency mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	524,738	513,082
Gross Unrealized Gains	360	727
Gross Unrealized Losses	(13,713)	(6,293)
Fair Value	511,385	507,516
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,552	14,031
Gross Unrealized Gains	7	69
Gross Unrealized Losses	(241)	(46)
Fair Value	12,318	14,054
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	58,027	59,718
Gross Unrealized Gains	0	16
Gross Unrealized Losses	(1,579)	(330)
Fair Value	$ 56,448	$ 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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