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Employee Benefit Plans (Fair Value and Allocation Of Plan Assets) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Bancorporation Plan      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 168,591 $ 152,084 $ 150,893
Bancorporation Plan | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 126,709 116,021  
Bancorporation Plan | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 41,882 36,063  
Bancorporation Plan | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Cash and equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 3,941 $ 3,839  
Actual % of Plan Assets 2.34% 2.49%  
Bancorporation Plan | Cash and equivalents | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 0.00% 0.00%  
Bancorporation Plan | Cash and equivalents | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 5.00% 1.00%  
Bancorporation Plan | Cash and equivalents | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 3,941 $ 3,839  
Bancorporation Plan | Cash and equivalents | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Cash and equivalents | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Equity Securities      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 26,892 $ 18,274  
Actual % of Plan Assets 70.00% 58.00%  
Bancorporation Plan | Equity Securities | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 30.00% 30.00%  
Bancorporation Plan | Equity Securities | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 70.00% 70.00%  
Bancorporation Plan | Equity Securities | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 26,892 $ 18,260  
Bancorporation Plan | Equity Securities | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 14  
Bancorporation Plan | Equity Securities | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 0 $ 0  
Bancorporation Plan | Debt Securities      
Defined Benefit Plan Disclosure [Line Items]      
Actual % of Plan Assets 25.00% 31.00%  
Bancorporation Plan | Debt Securities | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 15.00% 15.00%  
Bancorporation Plan | Debt Securities | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 45.00% 45.00%  
Bancorporation Plan | Equity mutual funds      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 90,466 $ 69,978  
Bancorporation Plan | Equity mutual funds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 84,954 68,832  
Bancorporation Plan | Equity mutual funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 5,512 1,146  
Bancorporation Plan | Equity mutual funds | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | US government and government agency securities      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 15,798 15,407  
Bancorporation Plan | US government and government agency securities | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | US government and government agency securities | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 15,798 15,407  
Bancorporation Plan | US government and government agency securities | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Corporate Bonds      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 20,572 19,496  
Bancorporation Plan | Corporate Bonds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Corporate Bonds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 20,572 19,496  
Bancorporation Plan | Corporate Bonds | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Fixed Income Mutual Funds      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 5,163 11,822  
Bancorporation Plan | Fixed Income Mutual Funds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 5,163 11,822  
Bancorporation Plan | Fixed Income Mutual Funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Fixed Income Mutual Funds | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Alternative investments      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 5,759 $ 13,268  
Actual % of Plan Assets 3.00%    
Bancorporation Plan | Alternative investments | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 0.00% 0.00%  
Bancorporation Plan | Alternative investments | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 30.00% 30.00%  
Bancorporation Plan | Alternative investments | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 5,759 $ 13,268  
Bancorporation Plan | Alternative investments | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
Bancorporation Plan | Alternative investments | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 712,999 $ 600,616 $ 550,025
Actual % of Plan Assets 100.00% 100.00%  
Employer contributions $ 50,000 $ 50,000  
BancShares Plan | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 547,193 470,211  
BancShares Plan | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 165,806 130,405  
BancShares Plan | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Cash and equivalents      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 67,084 $ 60,674  
Actual % of Plan Assets 9.00% 10.00%  
BancShares Plan | Cash and equivalents | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 0.00% 0.00%  
BancShares Plan | Cash and equivalents | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 5.00% 1.00%  
BancShares Plan | Cash and equivalents | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 67,084 $ 60,674  
BancShares Plan | Cash and equivalents | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Cash and equivalents | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Equity Securities      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 76,920 $ 66,015  
Actual % of Plan Assets 65.00% 54.00%  
BancShares Plan | Equity Securities | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 30.00% 30.00%  
BancShares Plan | Equity Securities | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 70.00% 70.00%  
BancShares Plan | Equity Securities | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 76,920 $ 65,964  
BancShares Plan | Equity Securities | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 51  
BancShares Plan | Equity Securities | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 0 $ 0  
BancShares Plan | Debt Securities      
Defined Benefit Plan Disclosure [Line Items]      
Actual % of Plan Assets 23.00% 28.00%  
BancShares Plan | Debt Securities | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 15.00% 15.00%  
BancShares Plan | Debt Securities | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 45.00% 45.00%  
BancShares Plan | Equity mutual funds      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 381,747 $ 256,976  
BancShares Plan | Equity mutual funds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 360,175 252,710  
BancShares Plan | Equity mutual funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 21,572 4,266  
BancShares Plan | Equity mutual funds | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | US government and government agency securities      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 60,663 57,890  
BancShares Plan | US government and government agency securities | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | US government and government agency securities | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 60,663 57,890  
BancShares Plan | US government and government agency securities | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Corporate Bonds      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 83,571 68,198  
BancShares Plan | Corporate Bonds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Corporate Bonds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 83,571 68,198  
BancShares Plan | Corporate Bonds | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Fixed Income Mutual Funds      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 20,497 42,849  
BancShares Plan | Fixed Income Mutual Funds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 20,497 42,849  
BancShares Plan | Fixed Income Mutual Funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Fixed Income Mutual Funds | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Alternative investments      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 22,517 $ 48,014  
Actual % of Plan Assets 3.00% 8.00%  
BancShares Plan | Alternative investments | Minimum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 0.00% 0.00%  
BancShares Plan | Alternative investments | Maximum      
Defined Benefit Plan Disclosure [Line Items]      
Target Allocation 30.00% 30.00%  
BancShares Plan | Alternative investments | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 22,517 $ 48,014  
BancShares Plan | Alternative investments | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets 0 0  
BancShares Plan | Alternative investments | Fair Value, Inputs, Level 3      
Defined Benefit Plan Disclosure [Line Items]      
Plan assets $ 0 $ 0