INVESTMENT AND MORTGAGE-BACKED SECURITIES - Securities Available-for-sale Major Categories (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Securities available-for-sale:
Amortized Cost	$ 1,574,094	$ 520,261
Gross Unrealized Gains	11,403	18,798
Gross Unrealized Losses	(21,786)	(198)
Fair Value	1,563,711	538,861
Agency Notes
Securities available-for-sale:
Amortized Cost	82,476	47,500
Gross Unrealized Gains		12
Gross Unrealized Losses	(2,222)	(91)
Fair Value	80,254	47,421
Treasury Securities
Securities available-for-sale:
Amortized Cost	247,916
Gross Unrealized Losses	(3,147)
Fair Value	244,769
Corporate Securities
Securities available-for-sale:
Amortized Cost	148,430	62,021
Gross Unrealized Gains	4,354	2,440
Gross Unrealized Losses	(754)
Fair Value	152,030	64,461
Pass-through mortgage-backed securities ("MBS") issued by government sponsored entities ("GSEs")
Securities available-for-sale:
Amortized Cost	528,749	135,842
Gross Unrealized Gains	4,271	7,672
Gross Unrealized Losses	(6,566)	(31)
Fair Value	526,454	143,483
Agency collateralized mortgage obligations ("CMOs")
Securities available-for-sale:
Amortized Cost	527,348	274,898
Gross Unrealized Gains	2,705	8,674
Gross Unrealized Losses	(8,795)	(76)
Fair Value	521,258	$ 283,496
State and municipal obligations.
Securities available-for-sale:
Amortized Cost	39,175
Gross Unrealized Gains	73
Gross Unrealized Losses	(302)
Fair Value	$ 38,946

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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