Debt Securities Held to Maturity - Expected Maturities of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized cost
Amortized cost	$ 285,756	$ 262,143
Fair value
Fair value	289,505	254,841
U.S. government and agency obligations
Amortized cost
More than ten years	20,000
Amortized cost	20,000	23,404
Fair value
More than ten years	19,960
Fair value	19,960	23,241
Mortgage-backed securities and collateralized mortgage obligations
Amortized cost
Amortized cost	265,756	238,739
Fair value
Fair value	$ 269,545	$ 231,600

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
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing after tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)(4)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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-Section 50
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Amount of investment in debt security, measured at amortized cost (held-to-maturity), with single maturity date and allocated without single maturity date, maturing after tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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

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