Investments - Schedule of Available-for-sale and Held-to-Maturity Securities Reconciliation (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	$ 346,436		$ 181,166
Gross Unrealized Gains	10,498		973
Gross Unrealized Losses	(150)		(200)
Allowance for Credit Losses	645	$ 0
Fair Value	356,139		181,939
Total securities held-to-maturity, net	345,791		181,166
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	960,984		1,115,323
Gross Unrealized Gains	37,259		21,548
Gross Unrealized Losses	(139)		(1,554)
Allowance for Credit Losses	0
Fair Value	998,104		1,135,317
Obligations of U.S. Government-sponsored enterprises
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,966		9,954
Gross Unrealized Gains	275		92
Gross Unrealized Losses	0		0
Allowance for Credit Losses	0
Fair Value	10,241		10,046
Obligations of states and political subdivisions
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	96,547		11,704
Gross Unrealized Gains	336		170
Gross Unrealized Losses	(122)		0
Allowance for Credit Losses	16
Fair Value	96,745		11,874
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	245,961		207,269
Gross Unrealized Gains	8,450		6,118
Gross Unrealized Losses	(133)		(363)
Allowance for Credit Losses	0
Fair Value	254,278		213,024
Agency mortgage-backed securities
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	127,353		46,346
Gross Unrealized Gains	2,469		675
Gross Unrealized Losses	(28)		0
Allowance for Credit Losses	0
Fair Value	129,794		47,021
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	693,082		888,129
Gross Unrealized Gains	27,915		15,083
Gross Unrealized Losses	(6)		(1,191)
Allowance for Credit Losses	0
Fair Value	720,991		902,021
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,975		9,971
Gross Unrealized Gains	591		255
Gross Unrealized Losses	0		0
Allowance for Credit Losses	0
Fair Value	10,566		10,226
Corporate Debt Securities [Member]
Debt Securities, Held-to-maturity [Abstract]
Amortized Cost	122,536		123,116
Gross Unrealized Gains	7,693		128
Gross Unrealized Losses	0		(200)
Allowance for Credit Losses	629
Fair Value	129,600		$ 123,044
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	2,000
Gross Unrealized Gains	28
Gross Unrealized Losses	0
Fair Value	$ 2,028

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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