Securities, Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Available-for-sale [Abstract]
Amortized cost	$ 1,524,014	$ 978,774
Gross unrealized gains	13,594	19,273
Gross unrealized losses	(11,870)	(786)
Fair value	1,525,738	997,261
U.S. Treasury and Government Agencies [Member]
Available-for-sale [Abstract]
Amortized cost	303,897	148,507
Gross unrealized gains	575	483
Gross unrealized losses	(2,062)	(197)
Fair value	302,410	148,793
State and Political Subdivisions [Member]
Available-for-sale [Abstract]
Amortized cost	335,389	133,287
Gross unrealized gains	5,548	7,132
Gross unrealized losses	(5,381)	(3)
Fair value	335,556	140,416
U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Available-for-sale [Abstract]
Amortized cost	784,733	640,537
Gross unrealized gains	7,070	11,648
Gross unrealized losses	(4,296)	(378)
Fair value	787,507	651,807
Asset-backed Securities [Member]
Available-for-sale [Abstract]
Amortized cost	99,995	56,443
Gross unrealized gains	401	10
Gross unrealized losses	(131)	(208)
Fair value	$ 100,265	$ 56,245

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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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