Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	$ 416,380
Available-for-sale, less than 12 months, gross unrealized losses	(2,912)
Available-for-sale, 12 months or more, estimated fair value	58,753
Available-for-sale, 12 months or more, gross unrealized losses	(929)
Available-for-sale, total, estimated fair value	475,133
Available-for-sale, total, gross unrealized losses	(3,841)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	213,014
Available-for-sale, less than 12 months, gross unrealized losses	(440)
Available-for-sale, 12 months or more, estimated fair value	54,329
Available-for-sale, 12 months or more, gross unrealized losses	(922)
Available-for-sale, total, estimated fair value	267,343
Available-for-sale, total, gross unrealized losses	(1,362)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	95,213
Available-for-sale, less than 12 months, gross unrealized losses	(433)
Available-for-sale, 12 months or more, estimated fair value	4,038
Available-for-sale, 12 months or more, gross unrealized losses	(6)
Available-for-sale, total, estimated fair value	99,251
Available-for-sale, total, gross unrealized losses	(439)
State and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	108,153
Available-for-sale, less than 12 months, gross unrealized losses	(2,039)
Available-for-sale, 12 months or more, estimated fair value	386
Available-for-sale, 12 months or more, gross unrealized losses	(1)
Available-for-sale, total, estimated fair value	108,539
Available-for-sale, total, gross unrealized losses	$ (2,040)

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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