LOANS, Past Due (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) Loan		Dec. 31, 2019 USD ($) Loan
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	$ 18,157	[1]	$ 11,091	[2]
Total past due	19,203		13,306
Current	5,188,071		5,327,232
Loans	$ 5,207,274		$ 5,340,538
Number of real estate loans more than 90 days past due on contractual balloon payment | Loan	1		2
30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	$ 6		$ 681
60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	7		1
Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	1,033		1,533
Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	8,073	[1]	1,007	[2]
Total past due	9,112		3,171
Current	4,865,390		4,999,183
Loans	4,874,502		5,002,354
Real Estate Loans [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		631
Real Estate Loans [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	6		0
Real Estate Loans [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	1,033		1,533
Real Estate Loans [Member] | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	6,685	[1]	794	[2]
Total past due	6,691		1,211
Current	170,064		147,218
Loans	176,755		148,429
Real Estate Loans [Member] | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		417
Real Estate Loans [Member] | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	6		0
Real Estate Loans [Member] | One- to-Four Family Residential, Including Condominium and Cooperative Apartment [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans [Member] | Multifamily Residential and Residential Mixed-Use [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	1,332	[1]	153	[2]
Total past due	1,332		1,536
Current	3,158,916		3,383,839
Loans	3,160,248		3,385,375
Real Estate Loans [Member] | Multifamily Residential and Residential Mixed-Use [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		214
Real Estate Loans [Member] | Multifamily Residential and Residential Mixed-Use [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans [Member] | Multifamily Residential and Residential Mixed-Use [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		1,169
Real Estate Loans [Member] | Commercial Real Estate and Commercial Mixed-Use [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	56	[1]	60	[2]
Total past due	1,089		424
Current	1,402,896		1,349,761
Loans	1,403,985		1,350,185
Real Estate Loans [Member] | Commercial Real Estate and Commercial Mixed-Use [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans [Member] | Commercial Real Estate and Commercial Mixed-Use [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans [Member] | Commercial Real Estate and Commercial Mixed-Use [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	1,033		364
Real Estate Loans [Member] | ADC [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	0	[1]	0	[2]
Total past due	0		0
Current	133,514		118,365
Loans	133,514		118,365
Real Estate Loans [Member] | ADC [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans [Member] | ADC [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans [Member] | ADC [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
C&I [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	10,082	[1]	10,082	[2]
Total past due	10,082		10,126
Current	321,734		326,286
Loans	331,816		336,412
C&I [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		44
C&I [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
C&I [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Consumer [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Non-accrual	2	[1]	2	[2]
Total past due	9		9
Current	947		1,763
Loans	956		1,772
Consumer [Member] | 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	6		6
Consumer [Member] | 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	1		1
Consumer [Member] | Loans 90 Days or More Past Due and Still Accruing Interest [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due	0		0
Real Estate Loans and C & I Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loans	$ 5,206,318		$ 5,338,766

[1] Includes all loans on non-accrual status regardless of the number of days such loans were delinquent as of March 31, 2020.

[2] Includes all loans on non-accrual status regardless of the number of days such loans were delinquent as of December 31, 2019.