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Investment Securities - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	$ 174,353
Available-for-sale investments, After 1 through 5 years	439,604
Available-for-sale investments, After 5 through 10 years	469,759
Available-for-sale investments, After ten years	4,232
Available-for-sale investments, Fair Value	$ 1,087,948	$ 879,240
Available-for-sale, Weighted average yield, One year or less (in hundredths)	1.87%
Available-for-sale , Weighted average yield,After 1 through 5 years (in hundredths)	2.28%
Available-for-sale, Weighted average yield,After 5 through 10 years (in hundredths)	1.69%
Available-for-sale , Weighted average yield,After ten years (in hundredths)	2.57%
Available-for-sale , Weighted average yield,Total (in hundredths)	1.96%
Available-for-sale, Full Tax-equivalent yield, One year or less (in hundredths)	2.06%
Available-for-sale, Full Tax-equivalent yield,After 1 through 5 years (in hundredths)	2.45%
Available-for-sale, Full Tax-equivalent yield, After 5 through 10 years (in hundredths)	1.94%
Available-for-sale, Full Tax-equivalent yield,After ten years (in hundredths)	3.52%
Available-for-sale, Full Tax-equivalent yield,Total (in hundredths)	2.17%
Held-to-maturity, Maturity [Abstract]
Held-to-maturity, One Year or less	$ 5,012
Held-to-maturity, After1 through 5 years	0
Held-to-maturity, After 5 through 10 years	0
Held-to-maturity, After ten years	2,033
Held-to-maturity	$ 7,045	5,016
Held To Maturity Weighted average yield, One year or less	2.06%
Held To Maturity Weighted average yield, After 1 through 5 years	0.00%
Held To Maturity Weighted average yield After 5 through 10 years	0.00%
Held To Maturity Weighted average yield After ten years	0.00%
Held To Maturity Weighted average yield ,Total	2.06%
Held To Maturity, Full tax-equivalent yield , One year or less	2.06%
Held To Maturity, Full tax-equivalent yield , After 1 through 5 years	0.00%
Held To Maturity, Full tax-equivalent yield , After 5 through 10 years	0.00%
Held To Maturity, Full tax-equivalent yield , After ten years	0.00%
Held To Maturity, Full tax-equivalent yield , Total	2.06%
U.S. Treasury Securities and Obligations of U.S. Government Corporations & Agencies
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	$ 105,823
Available-for-sale investments, After 1 through 5 years	54,392
Available-for-sale investments, After 5 through 10 years	11,315
Available-for-sale investments, After ten years	0
Available-for-sale investments, Fair Value	171,530	127,069
Held-to-maturity, Maturity [Abstract]
Held-to-maturity, One Year or less	5,012
Held-to-maturity, After1 through 5 years	0
Held-to-maturity, After 5 through 10 years	0
Held-to-maturity, After ten years	0
Held-to-maturity	5,012	5,016
Obligations of States and Political Subdivisions
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	29,540
Available-for-sale investments, After 1 through 5 years	71,481
Available-for-sale investments, After 5 through 10 years	152,466
Available-for-sale investments, After ten years	4,232
Available-for-sale investments, Fair Value	257,719	249,844
Mortgage-backed Securities: GSE Residential
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	26,948
Available-for-sale investments, After 1 through 5 years	293,661
Available-for-sale investments, After 5 through 10 years	301,343
Available-for-sale investments, After ten years	0
Available-for-sale investments, Fair Value	621,952	491,348
Other Securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	12,042
Available-for-sale investments, After 1 through 5 years	20,070
Available-for-sale investments, After 5 through 10 years	4,635
Available-for-sale investments, After ten years	0
Available-for-sale investments, Fair Value	36,747	$ 10,979
Annuity
Held-to-maturity, Maturity [Abstract]
Held-to-maturity, One Year or less	0
Held-to-maturity, After1 through 5 years	0
Held-to-maturity, After 5 through 10 years	0
Held-to-maturity, After ten years	2,033
Held-to-maturity	$ 2,033

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The yield on an available-for-sale government security, when the effect of reduced taxes are taken into account, for securities that mature. The full tax-equivalent yield show what yield a fully taxable security would have to give, in order to be equivalent to a tax free government security.

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