INVESTMENT SECURITIES - Composition, Repricing and Yield Information of Investment Securities Portfolio (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 786,516
Securities available-for-sale, one year or less, weighted average yield (percent)	2.45%
Securities available-for-sale, more than one year through five years, fair value	$ 133,909
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	4.74%
Securities available-for-sale, more than five years through ten years, fair value	$ 77,338
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	2.96%
Securities available-for-sale, more than ten years, fair value	$ 178,266
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.11%
Securities available-for-sale, fair value	$ 1,176,029
Securities available-for-sale, weighted average yield (percent)	2.68%
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 0
Securities available-for-sale, one year or less, weighted average yield (percent)	0.00%
Securities available-for-sale, more than one year through five years, fair value	$ 0
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than five years through ten years, fair value	$ 30,413
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	2.20%
Securities available-for-sale, more than ten years, fair value	$ 75,142
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.35%
Securities available-for-sale, fair value	$ 105,555
Securities available-for-sale, weighted average yield (percent)	2.31%
U.S. government agency and U.S. government sponsored enterprise collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 118,163
Securities available-for-sale, one year or less, weighted average yield (percent)	0.74%
Securities available-for-sale, more than one year through five years, fair value	$ 11,608
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	2.02%
Securities available-for-sale, more than five years through ten years, fair value	$ 25,579
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	1.63%
Securities available-for-sale, more than ten years, fair value	$ 45,786
Securities available-for-sale, more than ten years, weighted average yield (percent)	0.93%
Securities available-for-sale, fair value	$ 201,136
Securities available-for-sale, weighted average yield (percent)	0.96%
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 0
Securities available-for-sale, one year or less, weighted average yield (percent)	0.00%
Securities available-for-sale, more than one year through five years, fair value	$ 0
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than five years through ten years, fair value	$ 0
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than ten years, fair value	$ 57,174
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.79%
Securities available-for-sale, fair value	$ 57,174
Securities available-for-sale, weighted average yield (percent)	2.79%
Non-agency residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 0
Securities available-for-sale, one year or less, weighted average yield (percent)	0.00%
Securities available-for-sale, more than one year through five years, fair value	$ 0
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than five years through ten years, fair value	$ 0
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than ten years, fair value	$ 164
Securities available-for-sale, more than ten years, weighted average yield (percent)	6.14%
Securities available-for-sale, fair value	$ 164
Securities available-for-sale, weighted average yield (percent)	6.14%
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 668,353
Securities available-for-sale, one year or less, weighted average yield (percent)	2.73%
Securities available-for-sale, more than one year through five years, fair value	$ 0
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than five years through ten years, fair value	$ 0
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	0.00%
Securities available-for-sale, more than ten years, fair value	$ 0
Securities available-for-sale, more than ten years, weighted average yield (percent)	0.00%
Securities available-for-sale, fair value	$ 668,353
Securities available-for-sale, weighted average yield (percent)	2.73%
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 0
Securities available-for-sale, one year or less, weighted average yield (percent)	0.00%
Securities available-for-sale, more than one year through five years, fair value	$ 122,301
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	4.99%
Securities available-for-sale, more than five years through ten years, fair value	$ 21,346
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	5.64%
Securities available-for-sale, more than ten years, fair value	$ 0
Securities available-for-sale, more than ten years, weighted average yield (percent)	0.00%
Securities available-for-sale, fair value	$ 143,647
Securities available-for-sale, weighted average yield (percent)	5.08%