Benefit Plans Pension Fair Value Assets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 1,093,784	$ 964,774	$ 862,951
Defined Benefit Plan, Fair Value of Plan Assets excluding assets recorded at Net Asset Value	998,316	900,439
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	166,614	104,144
Company Stock
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3,767	2,620
U.S. Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	37,927	37,130
International Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	124,336	115,757
Emerging Markets Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	132,069	111,794
Fixed Income Securities, Corporate and Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	92,085	84,020
Fixed Income Mutual Funds, Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	44,848	38,945
Fixed Income Mutual Funds, Core Bond
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	136,172	178,589
Real Estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	132,953	109,765
Real Asset Mutual Funds, Commodities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	53,088	47,697
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	43,060	39,275
Other Types of Investments, Global Allocation Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	12,359	12,269
Other Types of Investments Insurance linked securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	19,038	18,434
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets excluding assets recorded at Net Asset Value	801,040	701,454
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	166,614	104,144
Fair Value, Inputs, Level 1 [Member] | Company Stock
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3,767	2,620
Fair Value, Inputs, Level 1 [Member] | U.S. Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	7,467	7,245
Fair Value, Inputs, Level 1 [Member] | International Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	83,309	62,569
Fair Value, Inputs, Level 1 [Member] | Emerging Markets Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	131,103	110,972
Fair Value, Inputs, Level 1 [Member] | Fixed Income Securities, Corporate and Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	92,085	84,020
Fair Value, Inputs, Level 1 [Member] | Fixed Income Mutual Funds, Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 1 [Member] | Fixed Income Mutual Funds, Core Bond
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	72,061	116,629
Fair Value, Inputs, Level 1 [Member] | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	117,089	95,580
Fair Value, Inputs, Level 1 [Member] | Real Asset Mutual Funds, Commodities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	53,088	47,697
Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	43,060	39,275
Fair Value, Inputs, Level 1 [Member] | Other Types of Investments, Global Allocation Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	12,359	12,269
Fair Value, Inputs, Level 1 [Member] | Other Types of Investments Insurance linked securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	19,038	18,434
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets excluding assets recorded at Net Asset Value	195,483	197,499
Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 2 [Member] | Company Stock
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 2 [Member] | U.S. Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	30,460	29,885
Fair Value, Inputs, Level 2 [Member] | International Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	41,027	53,188
Fair Value, Inputs, Level 2 [Member] | Emerging Markets Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	966	822
Fair Value, Inputs, Level 2 [Member] | Fixed Income Securities, Corporate and Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 2 [Member] | Fixed Income Mutual Funds, Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	43,055	37,459
Fair Value, Inputs, Level 2 [Member] | Fixed Income Mutual Funds, Core Bond
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	64,111	61,960
Fair Value, Inputs, Level 2 [Member] | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	15,864	14,185
Fair Value, Inputs, Level 2 [Member] | Real Asset Mutual Funds, Commodities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 2 [Member] | Other Types of Investments, Global Allocation Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 2 [Member] | Other Types of Investments Insurance linked securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets excluding assets recorded at Net Asset Value	1,793	1,486
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Company Stock
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | U.S. Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | International Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Emerging Markets Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Fixed Income Securities, Corporate and Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Fixed Income Mutual Funds, Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	1,793	1,486	$ 1,461
Fair Value, Inputs, Level 3 [Member] | Fixed Income Mutual Funds, Core Bond
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Real Asset Mutual Funds, Commodities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Other Types of Investments, Global Allocation Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value, Inputs, Level 3 [Member] | Other Types of Investments Insurance linked securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Fair Value Measured at Net Asset Value Per Share | International Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Net Asset Value Assets	2,930	3,288
Fair Value Measured at Net Asset Value Per Share | Emerging Markets Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Net Asset Value Assets	7,262	6,650
Fair Value Measured at Net Asset Value Per Share | Hedge Funds, Multi-strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 85,276	$ 54,397