INVESTMENT SECURITIES - Composition, Repricing and Yield Information of Investment Securities Portfolio (Details) $ in Thousands	Mar. 31, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 810,753
Securities available-for-sale, one year or less, weighted average yield (percent)	1.69%
Securities available-for-sale, more than one year through five years, fair value	$ 143,437
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	4.77%
Securities available-for-sale, more than five years through ten years, fair value	$ 99,206
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	2.40%
Securities available-for-sale, more than ten years, fair value	$ 217,434
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.28%
Securities available-for-sale, fair value	$ 1,270,830
Weighted-Average Yield	2.18%
SBA loan pool securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 16,733
Securities available-for-sale, one year or less, weighted average yield (percent)	1.34%
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	$ 16,733
Weighted-Average Yield	1.34%
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	$ 29,238
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	$ 94,062
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.35%
Securities available-for-sale, fair value	$ 123,300
Weighted-Average Yield	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	$ 110,147
Securities available-for-sale, one year or less, weighted average yield (percent)	0.67%
Securities available-for-sale, more than one year through five years, fair value	$ 11,193
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	1.99%
Securities available-for-sale, more than five years through ten years, fair value	$ 42,747
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	1.35%
Securities available-for-sale, more than ten years, fair value	$ 46,869
Securities available-for-sale, more than ten years, weighted average yield (percent)	1.76%
Securities available-for-sale, fair value	$ 210,956
Weighted-Average Yield	1.12%
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	$ 9,193
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	2.60%
Securities available-for-sale, more than ten years, fair value	$ 76,345
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.49%
Securities available-for-sale, fair value	$ 85,538
Weighted-Average Yield	2.51%
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	$ 158
Securities available-for-sale, more than ten years, weighted average yield (percent)	6.36%
Securities available-for-sale, fair value	$ 158
Weighted-Average Yield	6.36%
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 683,873
Securities available-for-sale, one year or less, weighted average yield (percent)	1.86%
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	$ 683,873
Weighted-Average Yield	1.86%
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	$ 132,244
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	5.01%
Securities available-for-sale, more than five years through ten years, fair value	$ 18,028
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	5.73%
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	$ 150,272
Weighted-Average Yield	5.08%

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Weighted average yield of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing after tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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