Retirement Plans, Fair Value of Pension Plan Investments Table (Details) - Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan Investments
RAP Investment Amount	$ 442,034	$ 390,564	$ 331,609
Fair Value, Inputs, Level 1
Pension Plan Investments
RAP Investment Amount	391,979	343,299
Fair Value, Inputs, Level 2
Pension Plan Investments
RAP Investment Amount	0	0
Fair Value, Inputs, Level 3
Pension Plan Investments
RAP Investment Amount	50,055	47,265
Money market account
Pension Plan Investments
RAP Investment Amount	8,903	7,159
Money market account | Fair Value, Inputs, Level 1
Pension Plan Investments
RAP Investment Amount	8,903	7,159
Money market account | Fair Value, Inputs, Level 2
Pension Plan Investments
RAP Investment Amount	0	0
Money market account | Fair Value, Inputs, Level 3
Pension Plan Investments
RAP Investment Amount	0	0
Common /collective trust funds
Pension Plan Investments
RAP Investment Amount	155,964	138,020
Common /collective trust funds | Fair Value, Inputs, Level 1
Pension Plan Investments
RAP Investment Amount	155,964	138,020
Common /collective trust funds | Fair Value, Inputs, Level 2
Pension Plan Investments
RAP Investment Amount	0	0
Common /collective trust funds | Fair Value, Inputs, Level 3
Pension Plan Investments
RAP Investment Amount	0	0
Mutual funds
Pension Plan Investments
RAP Investment Amount	227,112	198,120
Mutual funds | Fair Value, Inputs, Level 1
Pension Plan Investments
RAP Investment Amount	227,112	198,120
Mutual funds | Fair Value, Inputs, Level 2
Pension Plan Investments
RAP Investment Amount	0	0
Mutual funds | Fair Value, Inputs, Level 3
Pension Plan Investments
RAP Investment Amount	0	0
Group annuity contracts
Pension Plan Investments
RAP Investment Amount	50,055	47,265
Group annuity contracts | Fair Value, Inputs, Level 1
Pension Plan Investments
RAP Investment Amount	0	0
Group annuity contracts | Fair Value, Inputs, Level 2
Pension Plan Investments
RAP Investment Amount	0	0
Group annuity contracts | Fair Value, Inputs, Level 3
Pension Plan Investments
RAP Investment Amount	$ 50,055	$ 47,265