LOANS AND ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses and Recorded Investment Excluding Accrued Interest in Loans (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ 57,649
Provision for credit losses	$ 1,141	$ 11,826	$ 38,607	28,728	$ 38,805
Balance at end of period	90,927			90,927
Loans:
Individually evaluated for impairment	71,504		51,720	71,504	51,720
Collectively evaluated for impairment	5,606,498		6,331,539	5,606,498	6,331,539
Total	5,678,002		6,383,259	5,678,002	6,383,259	$ 5,951,885
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	94,565		63,818	61,713	66,814
Charge-offs	(1,821)		(35,546)	(3,897)	(39,060)
Recoveries of loans previously charged off	248		410	1,206	730
Net (charge-offs) recoveries	(1,573)		(35,136)	(2,691)	(38,330)
Provision for credit losses	1,141		38,607	28,728	38,805
Balance at end of period	94,133	94,565	67,289	94,133	67,289
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses			3,000
Loans:
Individually evaluated for impairment	28,475		22,042	28,475	22,042
Collectively evaluated for impairment	1,558,349		1,767,436	1,558,349	1,767,436
Total	1,586,824		1,789,478	1,586,824	1,789,478	1,691,270
Commercial | Commercial real estate
Loans:
Individually evaluated for impairment	6,471		0	6,471	0
Collectively evaluated for impairment	820,212		891,029	820,212	891,029
Total	826,683		891,029	826,683	891,029	818,817
Commercial | Multifamily
Loans:
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	1,476,803		1,563,757	1,476,803	1,563,757
Total	1,476,803		1,563,757	1,476,803	1,563,757	1,494,528
Commercial | SBA
Loans:
Individually evaluated for impairment	4,865		5,696	4,865	5,696
Collectively evaluated for impairment	315,708		69,663	315,708	69,663
Total	320,573		75,359	320,573	75,359	70,981
Commercial | Construction
Loans:
Individually evaluated for impairment	0		2,519	0	2,519
Collectively evaluated for impairment	197,629		226,042	197,629	226,042
Total	197,629		228,561	197,629	228,561	$ 231,350
Commercial | Lease Financing
Loans:
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			0		0
Total			0		0
Consumer | Single Family Residential Mortgage
Loans:
Individually evaluated for impairment	31,055		20,641	31,055	20,641
Collectively evaluated for impairment	1,203,424		1,755,312	1,203,424	1,755,312
Total	1,234,479		1,775,953	1,234,479	1,775,953
Consumer | Other Consumer
Loans:
Individually evaluated for impairment	638		822	638	822
Collectively evaluated for impairment	34,373		58,300	34,373	58,300
Total	35,011		59,122	35,011	59,122
Allowance for Loan Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	90,370		59,523	57,649	62,192
Charge-offs	(1,821)		(35,546)	(3,897)	(39,060)
Recoveries of loans previously charged off	248		410	1,206	730
Net (charge-offs) recoveries	(1,573)		(35,136)	(2,691)	(38,330)
Provision for credit losses	2,130		38,540	28,360	39,065
Balance at end of period	90,927	90,370	62,927	90,927	62,927
Individually evaluated for impairment	13,762		7,493	13,762	7,493
Collectively evaluated for impairment	77,165		55,434	77,165	55,434
Allowance for Loan Losses | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	90,370		59,523	57,649	62,192
Charge-offs	(1,821)		(35,546)	(3,897)	(39,060)
Recoveries of loans previously charged off	248		410	1,206	730
Net (charge-offs) recoveries	(1,573)		(35,136)	(2,691)	(38,330)
Provision for credit losses	2,130		38,540	28,360	39,065
Balance at end of period	90,927	90,370	62,927	90,927	62,927
Allowance for Loan Losses | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	26,618		21,529	22,353	18,191
Charge-offs	(1,597)		(34,673)	(2,761)	(36,788)
Recoveries of loans previously charged off	116		59	265	103
Net (charge-offs) recoveries	(1,481)		(34,614)	(2,496)	(36,685)
Provision for credit losses	1,454		37,660	6,072	43,069
Balance at end of period	26,591	26,618	24,575	26,591	24,575
Individually evaluated for impairment	11,162		4,614	11,162	4,614
Collectively evaluated for impairment	15,429		19,961	15,429	19,961
Allowance for Loan Losses | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	17,372		6,877	5,941	6,674
Charge-offs	0		0	0	0
Recoveries of loans previously charged off	0		0	0	0
Net (charge-offs) recoveries	0		0	0	0
Provision for credit losses	2,001		(298)	8,585	(95)
Balance at end of period	19,373	17,372	6,579	19,373	6,579
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	19,373		6,579	19,373	6,579
Allowance for Loan Losses | Commercial | Multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	25,105		12,625	11,405	17,970
Charge-offs	0		0	0	(6)
Recoveries of loans previously charged off	0		0	0	0
Net (charge-offs) recoveries	0		0	0	(6)
Provision for credit losses	454		(660)	12,345	(5,999)
Balance at end of period	25,559	25,105	11,965	25,559	11,965
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	25,559		11,965	25,559	11,965
Allowance for Loan Losses | Commercial | SBA
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4,184		3,120	3,120	1,827
Charge-offs	(224)		(738)	(580)	(1,086)
Recoveries of loans previously charged off	132		50	253	151
Net (charge-offs) recoveries	(92)		(688)	(327)	(935)
Provision for credit losses	(535)		1,686	376	3,226
Balance at end of period	3,557	4,184	4,118	3,557	4,118
Individually evaluated for impairment	2,409		2,858	2,409	2,858
Collectively evaluated for impairment	1,148		1,260	1,148	1,260
Allowance for Loan Losses | Commercial | Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	6,675		3,715	3,906	3,461
Charge-offs	0		0	0	0
Recoveries of loans previously charged off	0		0	0	0
Net (charge-offs) recoveries	0		0	0	0
Provision for credit losses	(470)		165	2,196	419
Balance at end of period	6,205	6,675	3,880	6,205	3,880
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	6,205		3,880	6,205	3,880
Allowance for Loan Losses | Commercial | Lease Financing
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0		0
Charge-offs			0		0
Recoveries of loans previously charged off			3		9
Net (charge-offs) recoveries			3		9
Provision for credit losses			(3)		(9)
Balance at end of period			0		0
Individually evaluated for impairment			0		0
Collectively evaluated for impairment			0		0
Allowance for Loan Losses | Consumer | Single Family Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	9,665		11,072	10,486	13,128
Charge-offs	0		(135)	(552)	(1,086)
Recoveries of loans previously charged off	0		0	639	150
Net (charge-offs) recoveries	0		(135)	87	(936)
Provision for credit losses	(689)		342	(1,177)	(913)
Balance at end of period	8,976	9,665	11,279	8,976	11,279
Individually evaluated for impairment	191		0	191	0
Collectively evaluated for impairment	8,785		11,279	8,785	11,279
Allowance for Loan Losses | Consumer | Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	751		585	438	941
Charge-offs	0		0	(4)	(94)
Recoveries of loans previously charged off	0		298	49	317
Net (charge-offs) recoveries	0		298	45	223
Provision for credit losses	(85)		(352)	(37)	(633)
Balance at end of period	666	$ 751	531	666	531
Individually evaluated for impairment	0		21	0	21
Collectively evaluated for impairment	$ 666		$ 510	666	510
Impact of adopting ASU 2016-13 | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				6,383	0
Impact of adopting ASU 2016-13 | Allowance for Loan Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				7,609
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				7,609	$ 0
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				662
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				4,847
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Commercial | Multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				1,809
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Commercial | SBA
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				388
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Commercial | Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				103
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Consumer | Single Family Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(420)
Impact of adopting ASU 2016-13 | Allowance for Loan Losses | Consumer | Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ 220