DERIVATIVE FINANCIAL INSTRUMENTS - Realized Investment Gains (Losses) - All other investments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Realized investment gains (losses) - all other investments
Modco trading portfolio	$ 18,552	$ 78,154

Amount of gain (loss) realized from securities classified as trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration