INVESTMENT SECURITIES - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) position	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Percentage of debt securities considered to be of investment-grade	98.00%
Percentage of tax-exempt municipal securities classified as pre-refunded	6.00%
General obligation bonds as percentage of tax-exempt municipal securities that were not pre-refunded	49.00%
Special revenue bonds as percentage of tax exempt municipal securities that were not pre-refunded	51.00%
Maximum percentage of any general obligation bonds in one state	9.00%
Percentage of tax-exempt securities insured by bond insurers	2.00%
Mortgage back securities as percent of agency mortgage-backed securities	93.00%	99.00%
Residential and commercial mortgage-backed securities, percentage of collateral consisting of prime loans	99.00%
Percentage of corporate securities associated with financial services industry	30.00%	23.00%
Number of securities in loss position	900
Number of positions	2,410
Other-than-temporary impairments | $	$ 0	$ 0	$ 0