SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 948,777	$ 947,597
Gross Unrealized Gains	11,375	10,480
Gross Unrealized (Losses)	(7,094)	(11,313)
Estimated Fair Value	953,058	946,764
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	274,003	274,007
Gross Unrealized Gains	5,910	4,962
Gross Unrealized (Losses)	(2,064)	(3,079)
Estimated Fair Value	277,849	275,890
Corporate and Other Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	112,432	123,674
Gross Unrealized Gains	775	892
Gross Unrealized (Losses)	(1,161)	(2,786)
Estimated Fair Value	112,046	121,780
Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	548,457	536,031
Gross Unrealized Gains	4,690	4,626
Gross Unrealized (Losses)	(3,792)	(5,371)
Estimated Fair Value	549,355	535,286
Other Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,885	13,885
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(77)	(77)
Estimated Fair Value	$ 13,808	$ 13,808