Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	$ 179,235		$ 181,166
Gross Unrealized Gains	2,239		973
Gross Unrealized Losses	(3,090)		(200)
Allowance for Credit Losses	303	$ 0
Fair Value	178,081		181,939
Total securities held-to-maturity, net	178,932		181,166
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,127,494		1,115,323
Gross Unrealized Gains	34,721		21,548
Gross Unrealized Losses	(701)		(1,554)
Allowance for Credit Losses	0
Fair Value	1,161,514		1,135,317
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,960		9,954
Gross Unrealized Gains	270		92
Gross Unrealized Losses	0		0
Allowance for Credit Losses	0
Fair Value	10,230		10,046
Obligations of states and political subdivisions
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	11,688		11,704
Gross Unrealized Gains	153		170
Gross Unrealized Losses	0		0
Allowance for Credit Losses	1
Fair Value	11,840		11,874
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	243,863		207,269
Gross Unrealized Gains	10,373		6,118
Gross Unrealized Losses	(205)		(363)
Allowance for Credit Losses	0
Fair Value	254,031		213,024
Agency mortgage-backed securities
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	44,720		46,346
Gross Unrealized Gains	1,924		675
Gross Unrealized Losses	0		0
Allowance for Credit Losses	0
Fair Value	46,644		47,021
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	863,698		888,129
Gross Unrealized Gains	23,465		15,083
Gross Unrealized Losses	(496)		(1,191)
Allowance for Credit Losses	0
Fair Value	886,667		902,021
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,973		9,971
Gross Unrealized Gains	613		255
Gross Unrealized Losses	0		0
Allowance for Credit Losses	0
Fair Value	10,586		10,226
Corporate Debt Securities [Member]
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	122,827		123,116
Gross Unrealized Gains	162		128
Gross Unrealized Losses	(3,090)		(200)
Allowance for Credit Losses	302
Fair Value	$ 119,597		$ 123,044

Debt Securities, Held-To-Maturity, Net Of Allowance For Credit Losses

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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