MORTGAGE SERVICING RIGHTS - Presentation of Activity Related to MSR (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Servicing Asset at Fair Value, Amount [Roll Forward]
Fair value, beginning of period	$ 596,378	$ 632,166	$ 580,860	$ 652,216
Change in fair value due to:
Changes in valuation inputs or assumptions	22,578	(9,205)	59,252	(15,438)
Other changes, including realization of expected cash flows	(19,942)	(17,098)	(41,098)	(31,128)
Fair value, end of period	599,014	605,653	599,014	605,653
Purchased Servicing Rights
Servicing Asset at Fair Value, Amount [Roll Forward]
Purchases (1)	$ 0	$ (210)	$ 0	$ 3