Quarterly report pursuant to Section 13 or 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
Sep. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 960,846 $ 947,597
Gross Unrealized Gains 12,942 10,480
Gross Unrealized (Losses) (5,427) (11,313)
Estimated Fair Value 968,361 946,764
Obligations of States and Political Subdivisions    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 285,921 274,007
Gross Unrealized Gains 7,582 4,962
Gross Unrealized (Losses) (1,304) (3,079)
Estimated Fair Value 292,199 275,890
Corporate and Other Bonds    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 114,997 123,674
Gross Unrealized Gains 1,241 892
Gross Unrealized (Losses) (816) (2,786)
Estimated Fair Value 115,422 121,780
Mortgage-Backed Securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 546,038 536,031
Gross Unrealized Gains 4,119 4,626
Gross Unrealized (Losses) (3,253) (5,371)
Estimated Fair Value 546,904 535,286
Other Securities    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 13,890 13,885
Gross Unrealized Gains 0 0
Gross Unrealized (Losses) (54) (77)
Estimated Fair Value $ 13,836 $ 13,808