Borrowings under Repurchase Agreements (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) counterparties	Dec. 31, 2017 USD ($) counterparties
Repurchase Agreements [Line Items]
Number of Counterparties with Outstanding Repurchase Agreements \| counterparties	15	15
Repurchase Agreements, collateral amount	$ 1,700,000	$ 1,700,000
Pledged Assets, Unsettled	$ 73,700	21,500
Repurchase Agreement Counterparty Concentration Risk Threshold	10.00%
Minimum [Member]
Repurchase Agreements [Line Items]
Repurchase Agreements Maturity	30 days
Maximum [Member]
Repurchase Agreements [Line Items]
Repurchase Agreements Maturity	180 days
Repurchase Agreements [Member]
Repurchase Agreements [Line Items]
Cash Collateral (Received) Pledged	$ 21,946	18,707
Security Owned and Pledged as Collateral, Fair Value	$ 2,100	$ 2,500

Number of counterparties with outstanding repurchase agreements at period end.

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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements which have been sold prior to period end but remain unsettled at the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Repurchase Agreement Counterparty Concentration Risk Threshold

+ References

No definition available.

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- Definition

[Line Items] for Repurchase Agreements [Table]

+ References

No definition available.

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- Definition

Repurchase Agreements Maturity

+ References

No definition available.

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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

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- Definition

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
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-Name Accounting Standards Codification
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-Section 50
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- Definition

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
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