INVESTMENTS (Narrative) (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Schedule of Investments [Line Items]
Net unrealized gains (losses) on available-for-sale securities, net of tax	$ 3,912,000		$ 3,912,000		$ (17,826,000)
Deferred tax assets, unrealized losses on available for sale securities	$ 1,100,000		1,100,000		$ 4,900,000
Payments to acquire investments			$ 98,800,000	$ 100,600,000
AFS securities in unrealized loss positions, number of positions | security	125		125		302
AFS and HTM securities in Continuous Unrealized Loss Position	$ 387,400,000		$ 387,400,000		$ 722,200,000
AFS and HTM Securities Unrealized Loss Accumulated in Investments	5,200,000		5,200,000		24,600,000
Fair Value - 12 Months of More	$ 387,390,000		$ 387,390,000		$ 621,294,000
Unrealized Loss as a Percent of Fair Value	1.40%		1.40%		3.40%
Carrying Value of Investments Sold	$ 45,800,000	$ 9,900,000	$ 45,800,000	9,900,000
Debt Securities, Available-for-sale, Gain (Loss)			27,000	31,000
Security pledged as collateral, amortized cost	667,300,000		667,300,000		$ 734,100,000
Security pledged as collateral, fair value	670,500,000		670,500,000		714,400,000
Unrealized loss, change in fair value of bank stock equity securities	(159,000)	11,000	84,000	$ (24,000)
Gain on sale of other investment		$ 195,000
Mortgage Backed Securities and Collateralized Mortgage Obligations
Schedule of Investments [Line Items]
AFS and HTM Securities Unrealized Loss Accumulated in Investments	5,200,000		5,200,000		23,300,000
Fair Value - 12 Months of More	383,300,000		383,300,000		591,900,000
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	246,463,000		246,463,000		364,430,000
Collateralized Mortgage Obligations
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	$ 136,876,000		$ 136,876,000		$ 227,461,000