UNSECURED BORROWINGS - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Junior subordinated notes maturity term	30 years
Face amount of junior subordinated notes	$ 100.0
Interest paid on unsecured borrowings	110.8	$ 79.1	$ 59.7
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Interest paid on unsecured borrowings	$ 7.5	$ 8.4	$ 8.4