Investment Securities - Securities With Unrealized Losses (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	$ 4,043
Held-to-maturity, less than 12 months, gross unrealized losses	(15)
Held-to-maturity, 12 months or more, estimated fair value	2,590
Held-to-maturity, 12 months or more, gross unrealized losses	(27)
Held-to-maturity, total, estimated fair value	6,633
Held-to-maturity, total, gross unrealized losses	(42)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	174,478
Available-for-sale, less than 12 months, gross unrealized losses	(605)
Available-for-sale, 12 months or more, estimated fair value	529,478
Available-for-sale, 12 months or more, gross unrealized losses	(4,410)
Available-for-sale, total, estimated fair value	703,956
Available-for-sale, total, gross unrealized losses	(5,015)
U.S. Government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	16,662
Available-for-sale, less than 12 months, gross unrealized losses	(36)
Available-for-sale, 12 months or more, estimated fair value	90,974
Available-for-sale, 12 months or more, gross unrealized losses	(1,166)
Available-for-sale, total, estimated fair value	107,636
Available-for-sale, total, gross unrealized losses	(1,202)
Mortgage-backed securities
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	3,408
Held-to-maturity, less than 12 months, gross unrealized losses	(15)
Held-to-maturity, 12 months or more, estimated fair value	2,575
Held-to-maturity, 12 months or more, gross unrealized losses	(27)
Held-to-maturity, total, estimated fair value	5,983
Held-to-maturity, total, gross unrealized losses	(42)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	133,538
Available-for-sale, less than 12 months, gross unrealized losses	(528)
Available-for-sale, 12 months or more, estimated fair value	435,207
Available-for-sale, 12 months or more, gross unrealized losses	(3,213)
Available-for-sale, total, estimated fair value	568,745
Available-for-sale, total, gross unrealized losses	(3,741)
State and political subdivisions
Held-to-Maturity
Held-to-maturity, less than 12 months, estimated fair value	635
Held-to-maturity, less than 12 months, gross unrealized losses	0
Held-to-maturity, 12 months or more, estimated fair value	15
Held-to-maturity, 12 months or more, gross unrealized losses	0
Held-to-maturity, total, estimated fair value	650
Held-to-maturity, total, gross unrealized losses	0
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, less than 12 months, estimated fair value	24,278
Available-for-sale, less than 12 months, gross unrealized losses	(41)
Available-for-sale, 12 months or more, estimated fair value	3,297
Available-for-sale, 12 months or more, gross unrealized losses	(31)
Available-for-sale, total, estimated fair value	27,575
Available-for-sale, total, gross unrealized losses	$ (72)

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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