LOANS HELD FOR INVESTMENT - Loan Portfolio Held for Investment (Parenthetical) (Detail) - Loans held for investmet [Member] - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, before Allowance for Credit Loss	$ 9,038,947	$ 9,002,205
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member]
Financing Receivable, before Allowance for Credit Loss	2,236,218	2,230,876
Commercial Portfolio Segment [Member] | Commercial And Industrial Sector [Member] | Commercial loans secured by real estate
Financing Receivable, before Allowance for Credit Loss	$ 712,600	$ 719,000