Pension Plans (Obligations and Funded Status) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Fair value of plan assets at beginning of year		$ 680,142
Fair value of plan assets at end of year		766,921		$ 680,142
Noncurrent liabilities		(69,610)		(97,246)
Qualified Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year		777,388		695,375
Service cost		5,234		5,100	$ 4,897
Interest cost		21,020		26,422	23,804
Actuarial liability loss gain (1)	[1]	72,145		88,271
Benefit payments		39,256		37,780
Projected benefit obligation at end of year		836,531		777,388	695,375
Fair value of plan assets at beginning of year		680,142		590,387
Actual return on plan assets		116,035		127,535
Employer contributions		10,000		0
Fair value of plan assets at end of year		766,921		680,142	590,387
Funded status at end of year		(69,610)		(97,246)
Accumulated benefit obligation		836,531		777,388
Current liabilities		0	[2]	0
Noncurrent liabilities		(69,610)		(97,246)
Total		(69,610)		(97,246)
Unrecognized loss		171,571		177,083
Amount included in accumulated other comprehensive income		171,571		177,083
SERP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year		7,336		6,913
Service cost		0		0	0
Interest cost		165		237	246
Actuarial liability loss gain (1)	[1]	702		720
Benefit payments		534		534
Projected benefit obligation at end of year		7,669		7,336	6,913
Fair value of plan assets at beginning of year		0		0
Actual return on plan assets		0		0
Employer contributions		534		534
Fair value of plan assets at end of year		0		0	$ 0
Funded status at end of year		(7,669)		(7,336)
Accumulated benefit obligation		7,669		7,336
Current liabilities		(2,771)		(528)
Noncurrent liabilities		(4,898)		(6,808)
Total		(7,669)		(7,336)
Unrecognized loss		1,069		1,311
Amount included in accumulated other comprehensive income		$ 1,069		$ 1,311

[1] The actuarial liability loss (gain) amount for the qualified pension plan for 2020 and 2019 is principally due to the effect of changes in the discount rate.

[2] (1) The current liabilities are included in other current liabilities on the Consolidated Balance Sheets