LOANS HELD FOR INVESTMENT - Corporation's TDR Activity (Detail) - TDR - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable Modifications [Line Items]
Beginning Balance of TDRs	$ 487,997	$ 582,647	$ 587,219
New TDRs	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)
Sales, net of charge-offs	0	0	0
Foreclosures	(2,015)	(12,872)	(21,591)
TDRs transferred from (to) held for sale	0	0	(34,541)
Paid-off and partial payments	(37,992)	(136,709)	(99,373)
Ending balance of TDRs	$ 479,196	$ 487,997	$ 582,647