Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 64,368	$ 65,679
Gross Unrealized Gains	102	16
Gross Unrealized Losses	(323)	(1,761)
Fair Value	64,147	63,934
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,095,529	733,279
Gross Unrealized Gains	8,822	1,487
Gross Unrealized Losses	(5,166)	(13,397)
Fair Value	1,099,185	721,369
US Treasury Bill Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,964	9,962
Gross Unrealized Gains	113	0
Gross Unrealized Losses	0	(37)
Fair Value	10,077	9,925
Obligations of U.S. Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,128	99,926
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(347)	(1,428)
Fair Value	53,781	98,498
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	114,770	26,566
Gross Unrealized Gains	2,218	327
Gross Unrealized Losses	(3)	(83)
Fair Value	116,985	26,810
Agency mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	895,899	596,825
Gross Unrealized Gains	6,461	1,160
Gross Unrealized Losses	(4,816)	(11,849)
Fair Value	897,544	586,136
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,768
Gross Unrealized Gains	30
Gross Unrealized Losses	0
Fair Value	20,798
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	12,490	12,506
Gross Unrealized Gains	91	16
Gross Unrealized Losses	(20)	(114)
Fair Value	12,561	12,408
Agency mortgage-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	51,878	53,173
Gross Unrealized Gains	11	0
Gross Unrealized Losses	(303)	(1,647)
Fair Value	$ 51,586	$ 51,526

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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