BORROWINGS - Summary of Short-Term Borrowings (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Securities sold under repurchase agreements	$ 280,492	$ 256,017
Federal Home Loan Bank advances	1,555,000	2,285,000
Federal funds purchased	1,830,000	1,000,000
Subordinated notes	136,988	137,320
Total short-term borrowings	$ 3,802,480	$ 3,678,337