Investment Securities - Amortized Cost and Fair Values of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Held-to-maturity:
Amortized Cost	$ 363,883	$ 371,517
Gross Unrealized Gains	8,436	2,684
Gross Unrealized Losses	(1,014)	(9,279)
Estimated Fair Value	371,305	364,922
Mortgage-backed securities
Held-to-maturity:
Amortized Cost	363,883	371,442
Gross Unrealized Gains	8,436	2,056
Gross Unrealized Losses	(1,014)	(9,279)
Estimated Fair Value	$ 371,305	364,219
Trust preferred securities
Held-to-maturity:
Amortized Cost		75
Gross Unrealized Gains		628
Estimated Fair Value		$ 703

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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