MORTGAGE SERVICING RIGHTS - Presentation of Activity Related to MSR (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Servicing Asset at Fair Value, Amount [Roll Forward]
Fair value, beginning of period	$ 599,014	$ 605,653	$ 580,860	$ 652,216
Other		0	0	10
Change in fair value due to:
Changes in valuation inputs or assumptions	(19,913)	(19,207)	(61,011)	(34,645)
Other changes, including realization of expected cash flows	9,732	(16,198)	68,984	(47,336)
Fair value, end of period	588,833	570,218	588,833	570,218
Purchased Servicing Rights
Servicing Asset at Fair Value, Amount [Roll Forward]
Purchases	$ 0	$ (30)	$ 0	$ (27)