Investment Securities - Available for Sale and Held for Maturity Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available-for-sale: [Abstract]
Amortized Cost	$ 1,209,831	$ 855,163
Gross Unrealized Gains	19,913	25,075
Gross Unrealized (Losses)	(7,546)	(998)
Fair Value	1,222,198	879,240
Held-to-maturity: [Abstract]
Held-to-maturity	7,049	5,016
Gross Unrealized Gains	56
Unrealized (Losses)	0
Fair Value	7,105	5,119
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies
Available-for-sale: [Abstract]
Amortized Cost	194,722	127,067
Gross Unrealized Gains	310	790
Gross Unrealized (Losses)	(2,853)	(788)
Fair Value	192,179	127,069
Held-to-maturity: [Abstract]
Held-to-maturity	5,008	5,016
Gross Unrealized Gains	56	103
Unrealized (Losses)	0	0
Fair Value	5,064	5,119
Obligations of States and Political Subdivisions
Available-for-sale: [Abstract]
Amortized Cost	294,255	237,886
Gross Unrealized Gains	11,751	11,995
Gross Unrealized (Losses)	(380)	(37)
Fair Value	305,626	249,844
Mortgage-backed Securities: GSE Residential
Available-for-sale: [Abstract]
Amortized Cost	685,736	479,470
Gross Unrealized Gains	7,119	12,038
Gross Unrealized (Losses)	(4,285)	(160)
Fair Value	688,570	491,348
Other Securities
Available-for-sale: [Abstract]
Amortized Cost	35,118	10,740
Gross Unrealized Gains	733	252
Gross Unrealized (Losses)	(28)	(13)
Fair Value	35,823	$ 10,979
Held-to-maturity: [Abstract]
Held-to-maturity	2,041
Gross Unrealized Gains	0
Unrealized (Losses)	0
Fair Value	$ 2,041

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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