Retirement Plans, Pension and Postretirement Plans Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair Value Of Plan Assets As A Percentage Of Net Benefit Obligation	171.00%	170.00%
RAP
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	$ 442,034	$ 390,564
Actual return on plan assets	58,802	67,377
Employer contributions	0	0
Gross benefits paid	(21,987)	(15,907)
Fair value of plan assets at end of year(a)	478,849	442,034	$ 390,564
Change in Benefit Obligation
Net benefit obligation at beginning of year	260,576	233,658
Service cost	8,244	7,263	7,540
Interest cost	8,185	9,752	9,125
Actuarial (gain) loss	24,998	25,810
Gross benefits paid	(21,987)	(15,907)
Net benefit obligation at end of year(a)	280,017	260,576	233,658
Funded (unfunded) status	198,832	181,458
Noncurrent assets	198,832	181,458
Current liabilities	0	0
Noncurrent liabilities	0	0
Asset (liability) recognized on the consolidated balance sheets	198,832	181,458
Postretirement Plan
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	210	270
Gross benefits paid	(210)	(270)
Fair value of plan assets at end of year(a)	0	0	0
Change in Benefit Obligation
Net benefit obligation at beginning of year	2,545	2,523
Service cost	0	0
Interest cost	78	104	108
Actuarial (gain) loss	(169)	188
Gross benefits paid	(210)	(270)
Net benefit obligation at end of year(a)	2,243	2,545	$ 2,523
Funded (unfunded) status	(2,243)	(2,545)
Noncurrent assets	0	0
Current liabilities	(189)	(214)
Noncurrent liabilities	(2,055)	(2,330)
Asset (liability) recognized on the consolidated balance sheets	$ (2,243)	$ (2,545)