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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 |

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