Investment Securities - Fair Value of Investments with Sustained Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	$ 435,007	$ 126,177
Available-for-sale, Less than 12 months, Unrealized Losses	(6,702)	(998)
Available-for-sale, 12 months or longer, Fair Value	121,550	2,377
Available-for-sale, 12 months or longer, Unrealized losses	(844)	0
Available-for-sale, Total Fair Value	556,557	128,554
Available-for-sale, Total Unrealized Losses	(7,546)	(998)
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	165,101	59,211
Available-for-sale, Less than 12 months, Unrealized Losses	(2,853)	(788)
Available-for-sale, 12 months or longer, Fair Value	0	0
Available-for-sale, 12 months or longer, Unrealized losses	0	0
Available-for-sale, Total Fair Value	165,101	59,211
Available-for-sale, Total Unrealized Losses	(2,853)	(788)
Obligations of States and Political Subdivisions
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	42,220	5,380
Available-for-sale, Less than 12 months, Unrealized Losses	(380)	(37)
Available-for-sale, 12 months or longer, Fair Value	0	0
Available-for-sale, 12 months or longer, Unrealized losses	0	0
Available-for-sale, Total Fair Value	42,220	5,380
Available-for-sale, Total Unrealized Losses	(380)	(37)
Mortgage-backed Securities: GSE Residential
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	219,104	57,609
Available-for-sale, Less than 12 months, Unrealized Losses	(3,441)	(160)
Available-for-sale, 12 months or longer, Fair Value	121,550	2,377
Available-for-sale, 12 months or longer, Unrealized losses	(844)	0
Available-for-sale, Total Fair Value	340,654	59,986
Available-for-sale, Total Unrealized Losses	(4,285)	(160)
Other Securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Less than 12 months, Fair Value	8,582	3,977
Available-for-sale, Less than 12 months, Unrealized Losses	(28)	(13)
Available-for-sale, 12 months or longer, Fair Value	0	0
Available-for-sale, 12 months or longer, Unrealized losses	0	0
Available-for-sale, Total Fair Value	8,582	3,977
Available-for-sale, Total Unrealized Losses	$ (28)	$ (13)

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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