SECURITIES (Narrative) (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) security	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) security
Schedule of Investments [Line Items]
Net unrealized gains (losses) on available-for-sale securities, net of tax	$ (5,165,000)		$ (5,165,000)		$ (6,085,000)
Deferred tax assets, unrealized losses on available for sale securities	$ 2,700,000		2,700,000		$ 3,300,000
Payments to acquire investments			$ 141,600,000	$ 140,700,000
AFS securities in unrealized loss positions, number of positions | security	177		177		209
AFS and HTM securities in Continuous Unrealized Loss Position	$ 633,700,000		$ 633,700,000		$ 658,500,000
AFS and HTM Securities Unrealized Loss Accumulated in Investments	9,700,000		9,700,000		13,200,000
Fair Value - 12 Months of More	$ 135,730,000		$ 135,730,000		$ 103,708,000
Unrealized Loss as a Percent of Fair Value	1.50%		1.50%		2.00%
Proceeds from Sale of Available-for-sale Securities	$ 20,269,000	$ 0	$ 20,269,000	84,000
Net gain on sale of securities	827,000	$ 0	827,000	4,000
Investment securities sold, carrying amount	19,400,000		19,400,000	80,000
Federal Home Loan Bank Stock	19,200,000		19,200,000		$ 17,800,000
Federal Reserve Bank Stock	5,400,000		5,400,000		5,400,000
Security pledged as collateral, amortized cost	714,000,000		714,000,000		597,300,000
Security pledged as collateral, fair value	707,200,000		707,200,000		589,700,000
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	135,700,000		135,700,000
Collateralized Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	103,700,000		103,700,000
Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
AFS and HTM Securities Unrealized Loss Accumulated in Investments	4,800,000		4,800,000		3,900,000
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	47,553,000		47,553,000		29,496,000
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Fair Value - 12 Months of More	$ 88,177,000		$ 88,177,000		$ 74,212,000
Available-for-sale Securities
Schedule of Investments [Line Items]
Payments to acquire investments				130,300,000
Held-to-maturity Securities
Schedule of Investments [Line Items]
Payments to acquire investments				$ 10,400,000