MORTGAGE SERVICING RIGHTS - Presentation of Activity Related to MSR (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Servicing Asset at Fair Value, Amount [Roll Forward]
Fair value, beginning of period	$ 580,860	$ 652,216
Change in fair value due to:
Changes in valuation inputs or assumptions	36,674	(6,233)
Other changes, including realization of expected cash flows	(21,156)	(14,030)
Fair value, end of period	596,378	632,166
Purchased Servicing Rights
Servicing Asset at Fair Value, Amount [Roll Forward]
Purchases	$ 0	$ 213