Investment Securities - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	$ 170,732
Available-for-sale investments, After 1 through 5 years	496,707
Available-for-sale investments, After 5 through 10 years	546,300
Available-for-sale investments, After ten years	8,459
Available-for-sale investments, Fair Value	$ 1,222,198	$ 879,240
Available-for-sale, Weighted average yield, One year or less (in hundredths)	1.64%
Available-for-sale , Weighted average yield,After 1 through 5 years (in hundredths)	2.14%
Available-for-sale, Weighted average yield,After 5 through 10 years (in hundredths)	1.65%
Available-for-sale , Weighted average yield,After ten years (in hundredths)	2.12%
Available-for-sale , Weighted average yield,Total (in hundredths)	1.85%
Available-for-sale, Full Tax-equivalent yield, One year or less (in hundredths)	1.80%
Available-for-sale, Full Tax-equivalent yield,After 1 through 5 years (in hundredths)	2.31%
Available-for-sale, Full Tax-equivalent yield, After 5 through 10 years (in hundredths)	1.90%
Available-for-sale, Full Tax-equivalent yield,After ten years (in hundredths)	2.72%
Available-for-sale, Full Tax-equivalent yield,Total (in hundredths)	2.06%
Held-to-maturity, Maturity [Abstract]
Held-to-maturity, One Year or less	$ 5,008
Held-to-maturity, After1 through 5 years	0
Held-to-maturity, After 5 through 10 years	0
Held-to-maturity, After ten years	2,041
Held-to-maturity	$ 7,049	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 and Agencies
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	$ 116,012
Available-for-sale investments, After 1 through 5 years	64,894
Available-for-sale investments, After 5 through 10 years	11,273
Available-for-sale investments, After ten years	0
Available-for-sale investments, Fair Value	192,179	127,069
Held-to-maturity, Maturity [Abstract]
Held-to-maturity, One Year or less	5,008
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	5,008	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	25,869
Available-for-sale investments, After 1 through 5 years	81,102
Available-for-sale investments, After 5 through 10 years	190,196
Available-for-sale investments, After ten years	8,459
Available-for-sale investments, Fair Value	305,626	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	18,751
Available-for-sale investments, After 1 through 5 years	326,494
Available-for-sale investments, After 5 through 10 years	343,325
Available-for-sale investments, After ten years	0
Available-for-sale investments, Fair Value	688,570	491,348
Other Securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale investments, One year or less	10,100
Available-for-sale investments, After 1 through 5 years	24,217
Available-for-sale investments, After 5 through 10 years	1,506
Available-for-sale investments, After ten years	0
Available-for-sale investments, Fair Value	35,823	$ 10,979
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	2,041
Held-to-maturity	$ 2,041