LOANS HELD FOR INVESTMENT - Corporation's TDR Activity (Detail) - TDR [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable Modifications [Line Items]
Beginning Balance of TDRs	$ 496,207	$ 582,389	$ 487,997	$ 582,647
New TDRs	3,187	22,111	31,733	54,531
Increases to existing TDRs	2,210	125	5,821	1,647
Charge-offs post modification	(4,548)	(2,505)	(8,063)	(7,418)
Foreclosures	(309)	(2,716)	(1,947)	(9,637)
Paid-off and partial payments	(8,132)	(103,566)	(26,926)	(125,932)
Ending balance of TDRs	$ 488,615	$ 495,838	$ 488,615	$ 495,838