INVESTMENTS (Narrative) (Detail)	3 Months Ended
	Mar. 31, 2019 USD ($) security	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) security
Schedule of Investments [Line Items]
Net unrealized gains (losses) on available-for-sale securities, net of tax	$ (6,927,000)		$ (17,826,000)
Deferred tax assets, unrealized losses on available for sale securities	1,900,000		$ 4,900,000
Payments to acquire investments	$ 26,700,000	$ 50,100,000
AFS securities in unrealized loss positions, number of positions | security	192		302
AFS and HTM securities in Continuous Unrealized Loss Position	$ 593,700,000		$ 722,200,000
AFS and HTM Securities Unrealized Loss Accumulated in Investments	13,800,000		24,600,000
Fair Value - 12 Months of More	$ 582,441,000		$ 621,294,000
Unrealized Loss as a Percent of Fair Value	2.30%		3.40%
Security pledged as collateral, amortized cost	$ 679,000,000		$ 734,100,000
Security pledged as collateral, fair value	671,600,000		714,400,000
Unrealized loss, change in fair value of bank stock equity securities	242,000	(35,000)
Gain on sale of other investment		195,000
Dividend Income, Operating	230,000	286,000
Mortgage Backed Securities and Collateralized Mortgage Obligations
Schedule of Investments [Line Items]
AFS and HTM Securities Unrealized Loss Accumulated in Investments	13,600,000		23,300,000
Fair Value - 12 Months of More	572,500,000		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	347,541,000		364,430,000
Collateralized Mortgage Obligations
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	224,959,000		$ 227,461,000
Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Gain (Loss) on Sale of Securities, Net	$ 0
Net gain on sale of securities		$ 0