FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 3) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2014	Dec. 31, 2015
Quantitative information
Available-for-sale investment securities, at fair value	$ 2,626,617	$ 3,773,226
Corporate debt securities: \| Non-investment grade
Quantitative information
Available-for-sale investment securities, at fair value	14,681	9,642
Fair Value, Measurements, Recurring \| Fair Value Measurements (Level 3)
Quantitative information
Available-for-sale investment securities, at fair value	6,528	0
Fair Value, Measurements, Recurring \| Embedded derivative liabilities \| Fair Value Measurements (Level 3)
Quantitative information
Derivative liabilities	(3,392)
Fair Value, Measurements, Recurring \| Embedded derivative liabilities \| Discounted cash flow \| Fair Value Measurements (Level 3)
Quantitative information
Derivative liabilities	$ (3,392)
Fair Value, Measurements, Recurring \| Embedded derivative liabilities \| Discounted cash flow \| Fair Value Measurements (Level 3) \| Minimum
Quantitative information
Credit risk	0.12%
Fair Value, Measurements, Recurring \| Embedded derivative liabilities \| Discounted cash flow \| Fair Value Measurements (Level 3) \| Maximum
Quantitative information
Credit risk	0.14%
Fair Value, Measurements, Recurring \| Embedded derivative liabilities \| Discounted cash flow \| Fair Value Measurements (Level 3) \| Weighted Average
Quantitative information
Credit risk	0.13%
Fair Value, Measurements, Recurring \| Corporate debt securities: \| Non-investment grade \| Fair Value Measurements (Level 3)
Quantitative information
Available-for-sale investment securities, at fair value	$ 6,528	$ 0
Fair Value, Measurements, Recurring \| Corporate debt securities: \| Non-investment grade \| Discounted cash flow \| Fair Value Measurements (Level 3)
Quantitative information
Available-for-sale investment securities, at fair value	$ 6,528
Loss severity	85.00%
Fair Value, Measurements, Recurring \| Corporate debt securities: \| Non-investment grade \| Discounted cash flow \| Fair Value Measurements (Level 3) \| Minimum
Quantitative information
Constant prepayment rate	0.00%
Constant default rate	0.75%
Discount margin	4.50%
Fair Value, Measurements, Recurring \| Corporate debt securities: \| Non-investment grade \| Discounted cash flow \| Fair Value Measurements (Level 3) \| Maximum
Quantitative information
Constant prepayment rate	1.00%
Constant default rate	1.20%
Discount margin	7.50%
Fair Value, Measurements, Recurring \| Corporate debt securities: \| Non-investment grade \| Discounted cash flow \| Fair Value Measurements (Level 3) \| Weighted Average
Quantitative information
Constant prepayment rate	0.73%
Constant default rate	0.87%
Loss severity	85.00%
Discount margin	6.94%

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Section 50
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Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a percentage, used as an input to measure fair value.

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Loss, including interest and principal, incurred on a defaulted security, expressed as a percentage of the original principal balance, used as an input to measure fair value.

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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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Percentage of likelihood a loan will not be repaid and instead default, used as an input to measure fair value.

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