Retirement Plans Retirement Plans, Fair Value Reconciliation of Level 3 Retirement Account Plan Investments (Details) - Pension Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of group annuity contract at end of period	$ 442,034	$ 390,564	$ 331,609
Fair Value, Inputs, Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of group annuity contract at end of period	50,055	47,265
Group annuity contracts
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of group annuity contract at end of period	50,055	47,265
Group annuity contracts | Fair Value, Inputs, Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of group annuity contract at beginning of period		47,265	$ 49,191
Return on plan assets	5,495	565
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Decrease for Settlement	(2,704)	(2,491)
Fair value of group annuity contract at end of period	$ 50,055	$ 47,265