LOANS HELD FOR INVESTMENT - Corporation's TDR Activity (Detail) - TDR [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable Modifications [Line Items]
Beginning Balance of TDRs	$ 497,295	$ 589,795	$ 487,997	$ 582,647
New TDRs	5,421	6,961	28,546	32,420
Increases to existing TDRs	3,508	347	3,611	1,522
Charge-offs post modification	(1,178)	(2,092)	(3,515)	(4,913)
Foreclosures	(27)	(3,278)	(1,638)	(6,921)
Paid-off and partial payments	(8,812)	(9,344)	(18,794)	(22,366)
Ending balance of TDRs	$ 496,207	$ 582,389	$ 496,207	$ 582,389