SECURITIES (Schedule of Unrealized Gross Losses and Estimated Fair values of Investment Securities) (Details) $ in Thousands	Mar. 31, 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	232	209
Fair Value - Less Than 12 Months	$ 586,429	$ 511,991
Unrealized Losses - Less Than 12 Months	(8,859)	(8,686)
Fair Value - 12 Months of More	98,729	103,708
Unrealized Losses - 12 Months or More	(4,235)	(3,850)
Fair Value	685,158	615,699
Unrealized losses	(13,094)	(12,536)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	45,174	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(713)	(631)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	45,174	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(713)	(631)
AFS and HTM securities in Continues Unrealized Loss Position	730,300	$ 658,500
Unrealized Loss as a Percent of Fair Value		2.00%
AFS and HTM Securities Unrealized Loss Accumulated in Investments	13,800	$ 13,200
Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - 12 Months of More	98,700	103,700
AFS and HTM Securities Unrealized Loss Accumulated in Investments	4,200	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	393,109	348,579
Unrealized Losses - Less Than 12 Months	(5,745)	(5,780)
Fair Value - 12 Months of More	28,177	29,496
Unrealized Losses - 12 Months or More	(1,285)	(1,335)
Fair Value	421,286	378,075
Unrealized losses	(7,030)	(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	193,320	163,412
Unrealized Losses - Less Than 12 Months	(3,114)	(2,906)
Fair Value - 12 Months of More	70,552	74,212
Unrealized Losses - 12 Months or More	(2,950)	(2,515)
Fair Value	263,872	237,624
Unrealized losses	(6,064)	(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	45,174	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(713)	(631)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	45,174	42,805
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (713)	$ (631)