INVESTMENT SECURITIES - Composition, Repricing and Yield Information of Investment Securities Portfolio (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 670,360
Securities available-for-sale, one year or less, weighted average yield (percent)	1.56%
Securities available-for-sale, more than one year through five years, fair value	$ 162,179
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	4.62%
Securities available-for-sale, more than five years through ten years, fair value	$ 105,449
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	2.42%
Securities available-for-sale, more than ten years, fair value	$ 365,380
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.11%
Securities available-for-sale, fair value	$ 1,303,368
Weighted-Average Yield	2.15%
SBA loan pool securities
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale, one year or less, fair value	$ 15,421
Securities available-for-sale, one year or less, weighted average yield (percent)	0.93%
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	$ 15,421
Weighted-Average Yield	0.93%
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	$ 29,294
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	$ 163,992
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.16%
Securities available-for-sale, fair value	$ 193,286
Weighted-Average Yield	2.17%
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	$ 105,662
Securities available-for-sale, one year or less, weighted average yield (percent)	0.63%
Securities available-for-sale, more than one year through five years, fair value	$ 10,978
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	1.97%
Securities available-for-sale, more than five years through ten years, fair value	$ 42,423
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	1.34%
Securities available-for-sale, more than ten years, fair value	$ 96,242
Securities available-for-sale, more than ten years, weighted average yield (percent)	1.75%
Securities available-for-sale, fair value	$ 255,305
Weighted-Average Yield	1.23%
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	$ 15,425
Securities available-for-sale, more than five years through ten years, weighted average yield (percent)	2.62%
Securities available-for-sale, more than ten years, fair value	$ 104,992
Securities available-for-sale, more than ten years, weighted average yield (percent)	2.37%
Securities available-for-sale, fair value	$ 120,417
Weighted-Average Yield	2.40%
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	$ 154
Securities available-for-sale, more than ten years, weighted average yield (percent)	6.36%
Securities available-for-sale, fair value	$ 154
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	$ 549,277
Securities available-for-sale, one year or less, weighted average yield (percent)	1.76%
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	$ 549,277
Weighted-Average Yield	1.76%
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	$ 151,201
Securities available-for-sale, more than one year through five years, weighted average yield (percent)	4.82%
Securities available-for-sale, more than five years through ten years, fair value	$ 18,307
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	$ 169,508
Weighted-Average Yield	4.91%

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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