Note 3 - Debt Securities - Held to Maturity Securities in Continuous Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Securities held to maturity, less than 12 months fair value
Securities held to maturity, less than 12 months unrealized losses
Securities held to maturity, 12 months or longer fair value	24,990
Securities held to maturity, 12 months or longer unrealized losses	(23)
Securities held to maturity, total fair value	24,990
Securities held to maturity, unrealized losses	(23)
US Government Agencies Debt Securities [Member]
Securities held to maturity, less than 12 months fair value
Securities held to maturity, less than 12 months unrealized losses
Securities held to maturity, 12 months or longer fair value	17,867
Securities held to maturity, 12 months or longer unrealized losses	(20)
Securities held to maturity, total fair value	17,867
Securities held to maturity, unrealized losses	(20)
Corporate Debt Securities [Member]
Securities held to maturity, less than 12 months fair value
Securities held to maturity, less than 12 months unrealized losses
Securities held to maturity, 12 months or longer fair value	7,123
Securities held to maturity, 12 months or longer unrealized losses	(3)
Securities held to maturity, total fair value	7,123
Securities held to maturity, unrealized losses	$ (3)

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

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 (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 2: 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=118939692&loc=d3e27290-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

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

+ References

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Data Type:	xbrli:monetaryItemType
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- Definition

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.

+ 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=118939692&loc=d3e27290-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

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- Definition

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

+ References

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- Definition

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

+ References

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