LOANS HELD FOR INVESTMENT, NET - Impaired Real Estate Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2020
Unpaid Principal Balance [Abstract]
With no related allowance recorded		$ 4,567
With related allowance recorded		12,502
Total		17,069
Recorded Investment [Abstract]
With no related allowance recorded		4,567
With related allowance recorded		12,502
Total		17,069
Related Allowance [Abstract]
Related allowance		6,474
Average Recorded Investment [Abstract]
With no related allowance recorded	$ 3,749
Total	13,831
Interest Income Recognized [Abstract]
With no related allowance recorded	7
Total	7
Real estate
Related Allowance [Abstract]
Related allowance		0
Real estate | One-to-four family residential and cooperative/condominium apartment
Average Recorded Investment [Abstract]
With no related allowance recorded	2,948
Real estate | Multifamily residential and residential mixed-use
Unpaid Principal Balance [Abstract]
With no related allowance recorded		1,863
Recorded Investment [Abstract]
With no related allowance recorded		1,863
Related Allowance [Abstract]
Related allowance		0
Average Recorded Investment [Abstract]
With no related allowance recorded	743
Interest Income Recognized [Abstract]
With no related allowance recorded	6
Real estate | Commercial real estate ("CRE")
Unpaid Principal Balance [Abstract]
With no related allowance recorded		2,704
Recorded Investment [Abstract]
With no related allowance recorded		2,704
Related Allowance [Abstract]
Related allowance		0
Average Recorded Investment [Abstract]
With no related allowance recorded	58
Interest Income Recognized [Abstract]
With no related allowance recorded	1
Commercial and industrial ("C&I")
Unpaid Principal Balance [Abstract]
With related allowance recorded		12,502
Recorded Investment [Abstract]
With related allowance recorded		12,502
Related Allowance [Abstract]
Related allowance		$ 6,474
Average Recorded Investment [Abstract]
With related allowance recorded	$ 10,082