SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Valuation of Investment Securities, Cash, and Deferred Policy Acquisition Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) primary_source	Dec. 31, 2017 USD ($) input_method	Dec. 31, 2016 USD ($)
Valuation of investment securities
Number of primary sources of information used for determining fair value | primary_source	1
Total number of primary sources of information available for determining fair value	3	3
Cash
Negative balances due to outstanding checks and drafts | $	$ 132.7	$ 132.7	$ 79.2
Minimum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest rate assumptions to compute liabilities for future policy benefits	1.00%	1.00%
Maximum
Liability for Future Policy Benefit, by Product Segment [Line Items]
Interest rate assumptions to compute liabilities for future policy benefits	7.80%	7.80%