Employee Benefit Plans (Fair Value and Allocation Of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 1,235,555	$ 976,072	$ 842,534
Actual % of Plan Assets	100.00%	100.00%
Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 991,128	$ 775,527
Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	244,427	200,545
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Cash and equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 37,913	$ 10,974
Actual % of Plan Assets	3.00%	1.00%
Cash and equivalents | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	0.00%
Cash and equivalents | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%
Cash and equivalents | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 37,913	$ 10,974
Cash and equivalents | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Cash and equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 144,924	$ 142,157
Actual % of Plan Assets	77.00%	73.00%
Equity securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	30.00%
Equity securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	70.00%
Equity securities | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 144,924	$ 142,157
Equity securities | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Equity securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	559,472	565,343
Equity mutual funds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	559,472	565,343
Equity mutual funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Equity mutual funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	$ 0
Exchange Traded Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	248,819
Exchange Traded Funds | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	248,819
Exchange Traded Funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0
Exchange Traded Funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 0
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Actual % of Plan Assets	20.00%	23.00%
Debt Securities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	15.00%
Debt Securities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	45.00%
US government and government agency securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 90,292	$ 78,175
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
US government and government agency securities | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	90,292	78,175
US government and government agency securities | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Plan assets	154,135	122,370
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
Corporate Bonds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets	154,135	122,370
Corporate Bonds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 0	0
Fixed Income Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets		25,288
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		25,288
Fixed Income Mutual Funds | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Fixed Income Mutual Funds | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Plan assets		$ 31,765
Actual % of Plan Assets		3.00%
Alternative investments | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	0.00%
Alternative investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	30.00%
Alternative investments | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets		$ 31,765
Alternative investments | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Defined Benefit Plan Disclosure [Line Items]
Plan assets		0
Alternative investments | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets		$ 0