LOANS HELD FOR INVESTMENT - Loan Restructuring and Effect on Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Thousands		12 Months Ended
Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Abstract]
Impact of adopting ASC 326		$ 230,800
Provision (release) for credit losses		168,717	$ 40,225	$ 59,253
Accounting Standards Update 2016-13 [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Loans and Leases Receivable Disclosure [Abstract]
Impact of adopting ASC 326	$ (434)
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Loans and Leases Receivable Disclosure [Abstract]
Provision (release) for credit losses		2,105	(1,496)	7,032
Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
Loans and Leases Receivable Disclosure [Abstract]
Provision (release) for credit losses		81,125	(1,697)	23,074
Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
Loans and Leases Receivable Disclosure [Abstract]
Provision (release) for credit losses		6,627	(13,696)	(8,440)
Entity Loan Modification Program [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	487,997	487,997	582,647	587,219
New TDRs loan splits		36,319	63,433	171,857
Increases to existing TDRs (disbursements)		6,009	1,840	7,027
Charge-offs post modification		(11,122)	(10,342)	(27,951)
Paid-off and partial payments		(37,992)	(136,709)	(99,373)
Ending balance of TDRs		479,196	487,997	582,647
Entity Loan Modification Program [Member] \| Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	4,321	4,321
Ending balance of TDRs		3,423	4,321
Entity Loan Modification Program [Member] \| Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	74,979	74,979
Paid-off and partial payments		(92,400)
Ending balance of TDRs		64,438	74,979
Entity Loan Modification Program [Member] \| Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	66,849	66,849
Ending balance of TDRs		80,482	66,849
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	51,228	51,228	33,840	35,577
New TDRs loan splits		0	20,059	32,104
Increases to existing TDRs (disbursements)		738	0	0
Charge-offs post modification		(3,087)	0	0
Paid-off and partial payments		(3,792)	(2,671)	(33,841)
Ending balance of TDRs		45,087	51,228	33,840
Loans and Leases Receivable Disclosure [Abstract]
Beginning balance	3,530	3,530	473	3,846
Provision (release) for credit losses		284	3,057	(10,789)
Charge-offs		(3,087)	0	(7,416)
Ending balance		401	3,530	473
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Loans and Leases Receivable Disclosure [Abstract]
Impact of adopting ASC 326		(326)
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	1,883	1,883	2,431	0
New TDRs loan splits		0	0	2,503
Increases to existing TDRs (disbursements)		0	0	0
Charge-offs post modification		0	0	0
Paid-off and partial payments		(321)	(548)	(72)
Ending balance of TDRs		1,562	1,883	2,431
Loans and Leases Receivable Disclosure [Abstract]
Beginning balance	0	0	0	0
Provision (release) for credit losses		0	0	0
Charge-offs		0	0	0
Ending balance		0	0	0
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Loans and Leases Receivable Disclosure [Abstract]
Impact of adopting ASC 326		0
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	22,749	22,749	3,003	3,098
New TDRs loan splits		0	20,059	29,601
Increases to existing TDRs (disbursements)		0	0	0
Charge-offs post modification		(3,087)	0	0
Paid-off and partial payments		(3,187)	(313)	(29,696)
Ending balance of TDRs		16,475	22,749	3,003
Loans and Leases Receivable Disclosure [Abstract]
Beginning balance	3,516	3,516	0	0
Provision (release) for credit losses		(14)	3,516	(7,416)
Charge-offs		(3,087)	0	(7,416)
Ending balance		0	3,516	0
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Commercial Portfolio Segment [Member] \| Mortgage Receivable [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Loans and Leases Receivable Disclosure [Abstract]
Impact of adopting ASC 326		(415)
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member]
Financing Receivable, Troubled Debt Restructuring [Abstract]
Beginning Balance of TDRs	26,596	26,596	28,406	32,479
New TDRs loan splits		0	0	0
Increases to existing TDRs (disbursements)		738	0	0
Charge-offs post modification		0	0	0
Paid-off and partial payments		(284)	(1,810)	(4,073)
Ending balance of TDRs		27,050	26,596	28,406
Loans and Leases Receivable Disclosure [Abstract]
Beginning balance	$ 14	14	473	3,846
Provision (release) for credit losses		298	(459)	(3,373)
Charge-offs		0	0	0
Ending balance		401	$ 14	$ 473
Entity Loan Modification Program [Member] \| AB Note Restructure Workout Strategy [Member] \| Commercial Portfolio Segment [Member] \| Commercial And Industrial Sector [Member] \| Accounting Standards Update 2016-13 [Member] \| Cumulative Effect, Period of Adoption, Adjustment [Member]
Loans and Leases Receivable Disclosure [Abstract]
Impact of adopting ASC 326		$ 89

Disbursements during the period on existing commitments of TDRs loans.

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Recorded investment in loans that were modified under troubled debt restructurings during the period.

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Repayments related to Trouble Debt Restructuring Loans.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of increase (decrease) in allowance for credit loss on financing receivable.

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Amount of financing receivable modified as troubled debt restructuring.

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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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Amount of expense related to estimated loss from loan and lease transactions.

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