LOANS RECEIVABLE AND THE ALLOWANCE FOR CREDIT LOSSES (Allowance for Loan Losses) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	$ 156,054	$ 167,279	$ 130,488	$ 167,279	$ 100,559
Provision/(recapture) for credit losses	(8,100)		29,524	(16,135)	51,237
Recoveries	593		642	2,105	3,008
Charge-offs	(538)		(4,302)	(5,240)	(6,264)
Allowance for loan losses, Ending balance	148,009	156,054	156,352	148,009	156,352
Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		7,812
Commercial Real Estate
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	59,411	57,791	29,339	57,791	30,591
Provision/(recapture) for credit losses	794		23,773	6,153	25,318
Recoveries	147		54	171	221
Charge-offs	(3)		0	(3,766)	(100)
Allowance for loan losses, Ending balance	60,349	59,411	53,166	60,349	53,166
Commercial Real Estate \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		(2,864)
Multifamily Real Estate
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	4,367	3,893	2,805	3,893	4,754
Provision/(recapture) for credit losses	1,440		699	1,914	1,020
Recoveries	0		0	0	0
Charge-offs	0		0	0	(66)
Allowance for loan losses, Ending balance	5,807	4,367	3,504	5,807	3,504
Multifamily Real Estate \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		(2,204)
Construction and Land
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	36,440	41,295	34,217	41,295	22,994
Provision/(recapture) for credit losses	(5,541)		2,694	(10,496)	11,402
Recoveries	0		105	100	105
Charge-offs	0		(100)	0	(100)
Allowance for loan losses, Ending balance	30,899	36,440	36,916	30,899	36,916
Construction and Land \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		2,515
Commercial Business
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	31,411	35,007	31,648	35,007	23,370
Provision/(recapture) for credit losses	(779)		5,405	(4,565)	11,852
Recoveries	321		370	1,300	575
Charge-offs	(123)		(3,553)	(912)	(4,937)
Allowance for loan losses, Ending balance	30,830	31,411	33,870	30,830	33,870
Commercial Business \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		3,010
Agricultural Business
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	4,617	4,914	4,513	4,914	4,120
Provision/(recapture) for credit losses	(1,367)		44	(1,664)	(962)
Recoveries	8		22	8	1,772
Charge-offs	(2)		(62)	(2)	(62)
Allowance for loan losses, Ending balance	3,256	4,617	4,517	3,256	4,517
Agricultural Business \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		(351)
One- to Four-Family Residential
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	7,988	9,913	11,884	9,913	4,136
Provision/(recapture) for credit losses	1,792		831	(246)	1,370
Recoveries	20		31	133	179
Charge-offs	0		0	0	(64)
Allowance for loan losses, Ending balance	9,800	7,988	12,746	9,800	12,746
One- to Four-Family Residential \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		7,125
Consumer
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	11,820	14,466	16,082	14,466	8,202
Provision/(recapture) for credit losses	(4,439)		(3,922)	(7,231)	1,237
Recoveries	97		60	393	156
Charge-offs	(410)		(587)	(560)	(935)
Allowance for loan losses, Ending balance	7,068	11,820	11,633	7,068	11,633
Consumer \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		2,973
Unallocated
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Allowance for loan losses, Beginning balance	0	0	0	0	2,392
Provision/(recapture) for credit losses	0		0	0	0
Recoveries	0		0	0	0
Charge-offs	0		0	0	0
Allowance for loan losses, Ending balance	$ 0	0	$ 0	$ 0	$ 0
Unallocated \| Impact of Adopting ASC 326
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision/(recapture) for credit losses		$ (2,392)

Amount of increase in allowance for credit loss on financing receivable from recovery.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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