CHANGE IN ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	$ 21	$ 320
Income taxes	(10,769)	(8,590)
Income before taxes	48,119	27,527
Net income	37,350	18,937
Prior service cost (credit), tax adjustment	100
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(76)	(330)
Reclassification out of Accumulated Other Comprehensive Income | Net change in defined benefit plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior service costs (credits) (1)	59	(19)
Transition obligation	0	0
Actuarial gains	(11)	(16)
Income taxes	11	12
Income before taxes	48	(35)
Net income	59	(23)
Reclassification out of Accumulated Other Comprehensive Income | Realized Gains on Securities Transactions | Net change in investment securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains on securities transactions	(21)	(320)
Income taxes	5	114
Net income	(16)	(206)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Net Unrealized Gains to Income During Period | Net change in investment securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of net unrealized gains to income during the period	(156)	(160)
Income taxes	37	59
Net income	$ (119)	$ (101)