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Borrowings under Repurchase Agreements Borrowings under Repurchase Agreements Schedule of Repurchase Agreement by Counterparty (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Repurchase Agreement Counterparty [Line Items]
Repurchase Agreement Counterparty Concentration Risk Threshold	10.00%
Repurchase Agreement Counterparty, Weighted Average Maturity of Agreements	49 days	43 days
Net Accrued Interest	$ 100
Wells Fargo Bank, N.A. [Member]
Repurchase Agreement Counterparty [Line Items]
Repurchase Agreement Counterparty, Amount at Risk	$ 17,085
Repurchase Agreement Counterparty, Weighted Average Maturity of Agreements	64 days
Repurchase Agreement Counterparty, Amount at Risk as a Percentage of Shareholders' Equity	10.00%

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- Definition

Net Accrued Interest

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- Definition

Repurchase Agreement Counterparty, Amount at Risk as a Percentage of Shareholders' Equity

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- Definition

Repurchase Agreement Counterparty Concentration Risk Threshold

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The amount at risk under repurchase agreements is defined as the excess of carrying amount (or market value, if higher than the carrying amount or if there is no carrying amount) of the securities or other assets sold under agreement to repurchase, including accrued interest plus any cash or other assets on deposit to secure the repurchase obligation, over the amount of the repurchase liability (adjusted for accrued interest).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(B)(iii))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Weighted average maturity (weighted by amount of the agreement) of repurchase agreements with the counterparty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(B)(iii))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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