FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 4) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2014	Sep. 30, 2015
Quantitative information
Available-for-sale investment securities, at fair value	$ 2,626,617	$ 2,952,277
Derivative liabilities	(56,493)	(98,748)
Corporate debt securities \| Non-investment grade
Quantitative information
Available-for-sale investment securities, at fair value	14,681	10,524
Fair Value, Measurements, Recurring
Quantitative information
Available-for-sale investment securities, at fair value	2,626,617	2,952,277
Fair Value, Measurements, Recurring \| Embedded derivative liabilities
Quantitative information
Derivative liabilities	(3,392)
Fair Value, Measurements, Recurring \| Corporate debt securities \| Non-investment grade
Quantitative information
Available-for-sale investment securities, at fair value	14,681	$ 10,524
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Quantitative information
Available-for-sale investment securities, at fair value	6,528
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Embedded derivative liabilities
Quantitative information
Derivative liabilities	(3,392)
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Non-investment grade
Quantitative information
Available-for-sale investment securities, at fair value	6,528
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Embedded derivative liabilities
Quantitative information
Derivative liabilities	$ (3,392)
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Embedded derivative liabilities \| Minimum
Quantitative information
Credit risk	0.12%
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Embedded derivative liabilities \| Maximum
Quantitative information
Credit risk	0.14%
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Embedded derivative liabilities \| Weighted Average
Quantitative information
Credit risk	0.13%
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Non-investment grade
Quantitative information
Available-for-sale investment securities, at fair value	$ 6,528
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Non-investment grade \| Minimum
Quantitative information
Constant prepayment rate	0.00%
Constant default rate	0.75%
Discount margin	4.50%
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Non-investment grade \| Maximum
Quantitative information
Constant prepayment rate	1.00%
Constant default rate	1.20%
Discount margin	7.50%
Fair Value, Measurements, Recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Non-investment grade \| Weighted Average
Quantitative information
Constant prepayment rate	0.73%
Constant default rate	0.87%
Loss severity	85.00%
Discount margin	6.94%

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

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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.

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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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