Retirement Benefits (Narrative) (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Postretirement And Other Retirement Plans [Line Items]
Mark-to-market actuarial net losses	$ 14,000	$ 13,300
Shares of company common stock	82.4	82.0	82.4	82.0
Unrealized gains included in earnings			$ 4,100	$ 3,900
Defined contribution plan vesting period			5 years
Defined contribution retirement plans expense			$ 3,200	3,700	$ 2,900
Fixed Income Securities [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Target allocation percentage for fixed income, equity and other investments	35.00%		35.00%
Equity Securities [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Target allocation percentage for fixed income, equity and other investments	60.00%		60.00%
Other Investments [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Target allocation percentage for fixed income, equity and other investments	5.00%		5.00%
Pension Plan [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Mark-to-market actuarial net losses			$ 10,900	1,200	16,600
Charge to remeasure liability based on lower discount rate			23,000	28,300
Actuarial gains					17,900
Gains (losses) from returns on plan assets			10,700	23,300	(31,000)
Gain on demographic experience and actuarial assumptions			$ 1,400	$ 3,800
Shares of company common stock	0.3	0.3	0.3	0.3
Market value of shares held of company common stock	$ 4,100	$ 4,200	$ 4,100	$ 4,200
Expected contribution to pension plans	15,000		15,000
Pension Plan [Member] | United States [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Mark-to-market actuarial net losses			10,938	1,228	16,633
Actuarial gains			(21,645)	(24,477)
Pension Plan [Member] | Non-U.S. Pension Plans [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Mark-to-market actuarial net losses			2,977	11,033	2,444
Charge to remeasure liability based on lower discount rate			5,900
Actuarial gains			(4,907)	(14,949)
Gain on demographic experience and actuarial assumptions			2,100
Expected contribution to pension plans	$ 2,600		2,600
Postretirement Health Care And Life Insurance Benefit Plans [Member]
Pension Postretirement And Other Retirement Plans [Line Items]
Mark-to-market actuarial net losses			101	1,080	$ (2,580)
Actuarial gains			$ (101)	$ (1,080)