SECURITIES - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) general_obligation_bonds	Sep. 30, 2017 USD ($)
Schedule Of Securities [Line Items]
Other than temporary impairment losses, investments, available-for-sale securities	$ 0	$ 0
Municipal bond portfolio, value	$ 1,000,000
Number of general obligation bond | general_obligation_bonds	1
Percentage of formal credit enhancement insurance of municipalities	64.00%
Municipal Bonds [Member] | Weighted Average [Member]
Schedule Of Securities [Line Items]
Average holding size of securities in bond portfolio	$ 3,100
Municipal Bonds [Member] | Credit Concentration Risk [Member] | General Obligation Bonds [Member] | A Rating [Member] | Minimum [Member]
Schedule Of Securities [Line Items]
Percentage of portfolio	100.00%
Municipal Bonds [Member] | Credit Concentration Risk [Member] | General Obligation Bonds [Member] | A Rating or Better [Member]
Schedule Of Securities [Line Items]
Percentage of portfolio	99.00%
Municipal Bonds [Member] | Geographic Concentration Risk [Member] | Pennsylvania, Ohio and Maryland [Member]
Schedule Of Securities [Line Items]
Percentage of portfolio	65.00%