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SECURITIES (Amortized Cost And Estimated Fair Values Of Available-For-Sale Securities) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost $ 2,531,402 $ 1,979,323 $ 2,521,592
Gross Unrealized Gains 20,181 37,372 21,407
Gross Unrealized Losses 10,696 322 11,323
Estimated Fair Value 2,540,887 2,016,373 2,531,676
Carrying value of FHLB stock 32,400 13,000  
Required investment in FHLB stock 27,200 6,500  
Gross gains recognized on available-for-sale securities 1,100 2  
US Government Agencies [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 1,823,294 1,190,199 1,794,231
Gross Unrealized Gains 861 5,974 1,261
Gross Unrealized Losses 5,975 6 6,065
Estimated Fair Value 1,818,180 1,196,167 1,789,427
U.S. Government Agency Issued Residential Mortgage-Backed Securities [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 167,986 187,410 176,476
Gross Unrealized Gains 1,389 2,582 1,665
Gross Unrealized Losses 1,833 251 1,898
Estimated Fair Value 167,542 189,741 176,243
U.S. Government Agency Issued Commercial Mortgage-Backed Securities [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 169,996 204,246 171,840
Gross Unrealized Gains 1,510 3,719 1,648
Gross Unrealized Losses 1,424 57 1,209
Estimated Fair Value 170,082 207,908 172,279
Obligations Of States And Political Subdivisions [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 337,595 384,326 346,609
Gross Unrealized Gains 16,193 24,219 15,547
Gross Unrealized Losses 1,464 8 2,151
Estimated Fair Value 352,324 408,537 360,005
FHLB and other securities [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Amortized Cost 32,531 13,142 32,436
Gross Unrealized Gains 228 878 1,286
Estimated Fair Value $ 32,759 $ 14,020 $ 33,722