COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Letters of Credit Facilities [Line Items]
Contractual Obligation, Future Minimum Payments Due, Remainder of Fiscal Year	$ 7,368
Amount of letters of credit issued	155,600	$ 255,400
Total equity securities, restricted cash, and cash and cash equivalents fair value pledged as security against the letters of credit	165,400	$ 310,900
Facility
Letters of Credit Facilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	600,000
Facility | Butterfield Bank (Cayman) Limited [Member]
Letters of Credit Facilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000
Notice period required for termination	90 days
Facility | Citibank Europe plc
Letters of Credit Facilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 400,000
Notice period required for termination	120 days
Facility | JP Morgan Chase Bank N.A.
Letters of Credit Facilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000
Notice period required for termination	120 days