Securities - Amortized Cost and Estimated Fair Value of Securities - Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Securities held-to-maturity:
Amortized Cost	$ 322,732		$ 366,560
Gross Unrealized Gains	9,721		2,519
Gross Unrealized (Losses)	(1)		(972)
Allowance for credit losses on debt securities	55	$ 58
Estimated Fair Value	332,452		368,107
Agency mortgage-backed securities
Securities held-to-maturity:
Amortized Cost	249,070		285,344
Gross Unrealized Gains	7,895		1,206
Gross Unrealized (Losses)	(1)		(968)
Estimated Fair Value	256,964		285,582
Municipals - exempt from Federal tax
Securities held-to-maturity:
Amortized Cost	73,662		81,216
Gross Unrealized Gains	1,826		1,313
Gross Unrealized (Losses)			(4)
Allowance for credit losses on debt securities	(55)
Estimated Fair Value	$ 75,488		$ 82,525

Not applicable.

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Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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