ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Net Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ (4,332)
Other comprehensive income before reclassification, net of tax			21,650	$ 12,475
Reclassifications from accumulated other comprehensive income, net of tax			175	571
Total other comprehensive income	$ 2,669	$ 857	21,825	13,046
Ending Balance	17,493		17,493
Unrealized Gains on Investments Available-for-Sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			4,000	(6,630)
Other comprehensive income before reclassification, net of tax			21,650	12,475
Reclassifications from accumulated other comprehensive income, net of tax			(322)	(15)
Total other comprehensive income			21,328	12,460
Ending Balance	25,328	5,830	25,328	5,830
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(8,332)	(9,124)
Other comprehensive income before reclassification, net of tax			0	0
Reclassifications from accumulated other comprehensive income, net of tax			497	586
Total other comprehensive income			497	586
Ending Balance	(7,835)	(8,538)	(7,835)	(8,538)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(4,332)	(15,754)
Total other comprehensive income	2,669	857	21,825	13,046
Ending Balance	$ 17,493	$ (2,708)	$ 17,493	$ (2,708)