FAIR VALUE - Valuation Techniques (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	$ 3,302,188	$ 45,179,906
Corporate investment – Limited partnership interests | Market approach (value of underlying assets) | Level III
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Total investments	26,581	25,750
Contingent consideration liability | Discounted cash flow | Level III
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Contingent consideration liability	$ (24,995)	$ (28,494)
Minimum | Contingent consideration liability | Discounted cash flow | Level III
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate (as a percent)	0.00%
Maximum | Contingent consideration liability | Discounted cash flow | Level III
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate (as a percent)	100.00%
Weighted Average | Contingent consideration liability | Discounted cash flow | Level III
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate (as a percent)	48.00%