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			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		$ 57,649		$ 57,649
Provision for (reversal of) credit losses	$ 11,826	15,761	$ (1,900)	27,587	$ 198
Balance at end of period	90,370			90,370
Loans:
Individually evaluated for impairment	75,225		48,400	75,225	48,400
Collectively evaluated for impairment	5,552,471		6,671,170	5,552,471	6,671,170
Total	5,627,696		6,719,570	5,627,696	6,719,570	$ 5,951,885
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	82,131	61,713	68,093	61,713	66,814
Charge-offs	0		(2,451)	(2,076)	(3,514)
Recoveries of loans previously charged off	608		76	958	320
Net (charge-offs) recoveries	608		(2,375)	(1,118)	(3,194)
Provision for (reversal of) credit losses	11,826		(1,900)	27,587	198
Balance at end of period	94,565	82,131	63,818	94,565	63,818
Commercial | Commercial and industrial
Loans:
Individually evaluated for impairment	31,129		20,429	31,129	20,429
Collectively evaluated for impairment	1,405,861		1,931,278	1,405,861	1,931,278
Total	1,436,990		1,951,707	1,436,990	1,951,707	1,691,270
Commercial | Commercial real estate
Loans:
Individually evaluated for impairment	5,168		0	5,168	0
Collectively evaluated for impairment	817,526		856,497	817,526	856,497
Total	822,694		856,497	822,694	856,497	818,817
Commercial | Multifamily
Loans:
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	1,434,071		1,598,978	1,434,071	1,598,978
Total	1,434,071		1,598,978	1,434,071	1,598,978	1,494,528
Commercial | SBA
Loans:
Individually evaluated for impairment	4,959		3,262	4,959	3,262
Collectively evaluated for impairment	305,825		77,667	305,825	77,667
Total	310,784		80,929	310,784	80,929	70,981
Commercial | Construction
Loans:
Individually evaluated for impairment	0		2,519	0	2,519
Collectively evaluated for impairment	212,979		206,510	212,979	206,510
Total	212,979		209,029	212,979	209,029	$ 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	32,999		21,021	32,999	21,021
Collectively evaluated for impairment	1,337,786		1,940,044	1,337,786	1,940,044
Total	1,370,785		1,961,065	1,370,785	1,961,065
Consumer | Other Consumer
Loans:
Individually evaluated for impairment	970		1,169	970	1,169
Collectively evaluated for impairment	38,423		60,196	38,423	60,196
Total	39,393		61,365	39,393	61,365
Allowance for Loan Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	78,243	57,649	63,885	57,649	62,192
Charge-offs	0		(2,451)	(2,076)	(3,514)
Recoveries of loans previously charged off	608		76	958	320
Net (charge-offs) recoveries	608		(2,375)	(1,118)	(3,194)
Provision for (reversal of) credit losses	11,519		(1,987)	26,230	525
Balance at end of period	90,370	78,243	59,523	90,370	59,523
Individually evaluated for impairment	12,575		2,824	12,575	2,824
Collectively evaluated for impairment	77,795		56,699	77,795	56,699
Allowance for Loan Losses | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	78,243	57,649	63,885	57,649	62,192
Charge-offs	0		(2,451)	(2,076)	(3,514)
Recoveries of loans previously charged off	608		76	958	320
Net (charge-offs) recoveries	608		(2,375)	(1,118)	(3,194)
Provision for (reversal of) credit losses	11,519		(1,987)	26,230	525
Balance at end of period	90,370	78,243	59,523	90,370	59,523
Allowance for Loan Losses | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	23,573	22,353	18,893	22,353	18,191
Charge-offs	0		(2,022)	(1,164)	(2,115)
Recoveries of loans previously charged off	119		11	149	44
Net (charge-offs) recoveries	119		(2,011)	(1,015)	(2,071)
Provision for (reversal of) credit losses	2,926		4,647	4,618	5,409
Balance at end of period	26,618	23,573	21,529	26,618	21,529
Individually evaluated for impairment	9,697		1,239	9,697	1,239
Collectively evaluated for impairment	16,921		20,290	16,921	20,290
Allowance for Loan Losses | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	13,620	5,941	6,838	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 (reversal of) credit losses	3,752		39	6,584	203
Balance at end of period	17,372	13,620	6,877	17,372	6,877
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	17,372		6,877	17,372	6,877
Allowance for Loan Losses | Commercial | Multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	20,072	11,405	18,898	11,405	17,970
Charge-offs	0		(6)	0	(6)
Recoveries of loans previously charged off	0		0	0	0
Net (charge-offs) recoveries	0		(6)	0	(6)
Provision for (reversal of) credit losses	5,033		(6,267)	11,891	(5,339)
Balance at end of period	25,105	20,072	12,625	25,105	12,625
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	25,105		12,625	25,105	12,625
Allowance for Loan Losses | Commercial | SBA
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	3,652	3,120	3,057	3,120	1,827
Charge-offs	0		8	(356)	(348)
Recoveries of loans previously charged off	0		60	121	101
Net (charge-offs) recoveries	0		68	(235)	(247)
Provision for (reversal of) credit losses	532		(5)	911	1,540
Balance at end of period	4,184	3,652	3,120	4,184	3,120
Individually evaluated for impairment	2,878		1,563	2,878	1,563
Collectively evaluated for impairment	1,306		1,557	1,306	1,557
Allowance for Loan Losses | Commercial | Construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7,052	3,906	3,453	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 (reversal of) credit losses	(377)		262	2,666	254
Balance at end of period	6,675	7,052	3,715	6,675	3,715
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	6,675		3,715	6,675	3,715
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		6
Net (charge-offs) recoveries			3		6
Provision for (reversal of) credit losses			(3)		(6)
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	9,593	10,486	12,142	10,486	13,128
Charge-offs	0		(425)	(552)	(951)
Recoveries of loans previously charged off	488		0	639	150
Net (charge-offs) recoveries	488		(425)	87	(801)
Provision for (reversal of) credit losses	(416)		(645)	(488)	(1,255)
Balance at end of period	9,665	9,593	11,072	9,665	11,072
Individually evaluated for impairment	0		0	0	0
Collectively evaluated for impairment	9,665		11,072	9,665	11,072
Allowance for Loan Losses | Consumer | Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	681	438	604	438	941
Charge-offs	0		(6)	(4)	(94)
Recoveries of loans previously charged off	1		2	49	19
Net (charge-offs) recoveries	1		(4)	45	(75)
Provision for (reversal of) credit losses	69		(15)	48	(281)
Balance at end of period	751	681	585	751	585
Individually evaluated for impairment	0		22	0	22
Collectively evaluated for impairment	$ 751		$ 563	751	563
Impact of adopting ASU 2016-13 | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		6,383		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		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		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		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		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		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		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		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)		(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		$ 220