LOANS AND ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses (Detail) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 01, 2020	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				$ 57,649
Provision for credit losses		$ 1,141	$ 11,826	$ 38,607	28,728	$ 38,805
Balance at end of period	$ 57,649	90,927			$ 90,927		$ 57,649
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member				us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201613Member
Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 61,713	94,565		63,818	$ 61,713	66,814	$ 66,814
Charge-offs		(1,821)		(35,546)	(3,897)	(39,060)
Recoveries		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	61,713
Impact of adopting ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at end of period	7,609
Impact of adopting ASU 2016-13 | Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	6,383				6,383	0	0
Balance at end of period							6,383
Allowance for Loan Losses
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	57,649	90,370		59,523	57,649	62,192	62,192
Charge-offs		(1,821)		(35,546)	(3,897)	(39,060)
Recoveries		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	57,649
Allowance for Loan Losses | Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	57,649	90,370		59,523	57,649	62,192	62,192
Charge-offs		(1,821)		(35,546)	(3,897)	(39,060)
Recoveries		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	57,649
Allowance for Loan Losses | Impact of adopting ASU 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7,609				7,609
Balance at end of period							7,609
Allowance for Loan Losses | Impact of adopting ASU 2016-13 | Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7,609				7,609	0	0
Balance at end of period							7,609
Reserve for Unfunded Loan Commitments | Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4,064	4,195		4,295	4,064	4,622	4,622
Charge-offs		0		0	0	0
Recoveries		0		0	0	0
Net (charge-offs) recoveries		0		0	0	0
Provision for credit losses		(989)		67	368	(260)
Balance at end of period		$ 3,206	$ 4,195	$ 4,362	3,206	4,362	4,064
Reserve for Unfunded Loan Commitments | Impact of adopting ASU 2016-13 | Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ (1,226)				$ (1,226)	$ 0	0
Balance at end of period							$ (1,226)