Investment Securities - Securities Held to Maturity in an Unrealized Loss Position (Details) - Mortgage-backed securities - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Held to maturity securities, less than 12 months, fair value	$ 4,900	$ 2,756
Held to maturity securities, less than 12 months, unrealized losses	(167)	(25)
Held to maturity securities, 12 months or longer, fair value	2,647	3,866
Held to maturity securities, 12 months or longer, unrealized losses	(124)	(61)
Held to maturity securities, fair value	7,547	6,622
Held to maturity securities, unrealized losses	$ (291)	$ (86)

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for less than 12 months.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer.

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