Annual report pursuant to Section 13 and 15(d)

SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details)

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SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Available-for-sale Securities, Amortized Cost Basis, Total $ 971,339 $ 947,597
Gross Unrealized Gains 10,569 10,480
Gross Unrealized (Losses) (7,686) (11,313)
Available for sale securities, Estimated fair value 974,222 946,764
Obligations of states and political subdivisions    
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Available-for-sale Securities, Amortized Cost Basis, Total 295,546 274,007
Gross Unrealized Gains 6,842 4,962
Gross Unrealized (Losses) (564) (3,079)
Available for sale securities, Estimated fair value 301,824 275,890
Corporate bonds    
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Available-for-sale Securities, Amortized Cost Basis, Total 113,625 123,674
Gross Unrealized Gains 1,131 892
Gross Unrealized (Losses) (876) (2,786)
Available for sale securities, Estimated fair value 113,880 121,780
Mortgage-backed securities    
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Available-for-sale Securities, Amortized Cost Basis, Total 552,431 536,031
Gross Unrealized Gains 2,596 4,626
Gross Unrealized (Losses) (6,169) (5,371)
Available for sale securities, Estimated fair value 548,858 535,286
Other securities    
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Available-for-sale Securities, Amortized Cost Basis, Total 9,737 13,885
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) (77) (77)
Available for sale securities, Estimated fair value $ 9,660 $ 13,808