DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018 USD ($) advance	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Federal home loan bank, number of advances | advance	7
Notional amount	$ 6,566,893,000		$ 5,628,119,000
Additional amount in excess of posted collateral required in case of breached agreements	$ 400,000		900,000
Interest rate contracts [Member]
Derivative [Line Items]
Maximum length of time hedged in interest rate cash flow hedge	5 years
Period to reclassification of cash flow hedge gain loss	12 months
Derivative gains to be reclassified within twelve months	$ 4,100,000
Derivative gains to be reclassified within twelve months, net of tax	3,200,000
Derivative gain or loses excluded from assessment of hedge effectiveness	0
Hedge ineffectiveness	0	$ 0
Gains or losses from cash flow hedge derivatives reclassified to earnings	0	$ 0
Credit risk contracts - not designated [Member]
Derivative [Line Items]
Notional amount	121,700,000
Maximum exposure under credit risk agreement assuming customer default	100,000		100,000
Credit risk derivatives, purchased at fair value	0		40,000
Credit risk derivatives, sold at fair value	$ 50,000		$ 100,000
Credit risk contracts - not designated [Member] | Minimum [Member]
Derivative [Line Items]
Risk participation agreements, term	2 months
Credit risk contracts - not designated [Member] | Maximum [Member]
Derivative [Line Items]
Risk participation agreements, term	9 years