SECURITIES (Schedule of Unrealized Gross Losses and Estimated Fair values of Investment Securities) (Details) $ in Thousands	Sep. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	177	209
Fair Value - Less Than 12 Months	$ 480,390	$ 511,991
Unrealized Losses - Less Than 12 Months	(4,706)	(8,686)
Fair Value - 12 Months of More	135,730	103,708
Unrealized Losses - 12 Months or More	(4,751)	(3,850)
Fair Value	616,120	615,699
Unrealized losses	(9,457)	(12,536)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	15,234	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(193)	(631)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	2,361	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(89)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	17,595	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(282)	(631)
AFS and HTM securities in Continuous Unrealized Loss Position	$ 633,700	$ 658,500
Unrealized Loss as a Percent of Fair Value	1.50%	2.00%
AFS and HTM Securities Unrealized Loss Accumulated in Investments	$ 9,700	$ 13,200
Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
AFS and HTM Securities Unrealized Loss Accumulated in Investments	4,800	3,900
Mortgage-backed securities issued or guaranteed by U.S. government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	345,629	348,579
Unrealized Losses - Less Than 12 Months	(3,127)	(5,780)
Fair Value - 12 Months of More	47,553	29,496
Unrealized Losses - 12 Months or More	(1,493)	(1,335)
Fair Value	393,182	378,075
Unrealized losses	(4,620)	(7,115)
Collateralized mortgage obligations issued or guaranteed by U.S. government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	134,761	163,412
Unrealized Losses - Less Than 12 Months	(1,579)	(2,906)
Fair Value - 12 Months of More	88,177	74,212
Unrealized Losses - 12 Months or More	(3,258)	(2,515)
Fair Value	222,938	237,624
Unrealized losses	(4,837)	(5,421)
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	15,234	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(193)	(631)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	2,361	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(89)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	17,595	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (282)	$ (631)