BORROWINGS - Significant Counterparties of Repurchase Agreements (Details)	12 Months Ended
Dec. 31, 2017 USD ($)
Repurchase Agreement Counterparty [Line Items]
Amount Outstanding	$ 1,234,522,000
Percent of total amount outstanding	100.00%
Weighted days to maturity	13 days
Market Value of collateral held	$ 1,295,225,428
North America
Repurchase Agreement Counterparty [Line Items]
Amount Outstanding	$ 939,438,000
Percent of total amount outstanding	76.10%
Weighted days to maturity	13 days
Market Value of collateral held	$ 985,672,703
Asia
Repurchase Agreement Counterparty [Line Items]
Amount Outstanding	$ 292,529,000
Percent of total amount outstanding	23.70%
Weighted days to maturity	14 days
Market Value of collateral held	$ 305,152,946
Europe
Repurchase Agreement Counterparty [Line Items]
Amount Outstanding	$ 2,555,000
Percent of total amount outstanding	0.20%
Weighted days to maturity	78 days
Market Value of collateral held	$ 4,399,779

It represents percentage of individual securities to total outstanding.

No definition available.

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- Definition

Fair value of collateral permitted, by contact or custom, to be sold or re-pledged.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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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

+ Details

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- Definition

Carrying value, as of the balance sheet date, of securities sold under agreements to repurchase where the transferor maintains effective control over the assets, accounting for them as secured debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 10
-Section 55
-Paragraph 51
-URI http://asc.fasb.org/extlink&oid=109221364&loc=d3e101761-111710

Reference 2: 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))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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- Details

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