SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Mortgage Banking Activities
Co-broker fees	$ 5.1	$ 5.7	$ 20.4	$ 13.9