Retirement Benefits (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,041,000	$ 2,276,000	$ 6,052,000	$ 4,553,000
Interest cost	2,563,000	2,930,000	5,046,000	5,860,000
Expected return on plan assets	(5,197,000)	(5,016,000)	(10,394,000)	(10,031,000)
Amortization of net (income) loss	2,462,000	1,601,000	3,675,000	3,203,000
Settlement charge		104,000		208,000
Net periodic benefit cost	1,869,000	1,895,000	4,379,000	3,793,000
Pension contributions	0	0	0	0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	311,000	286,000	452,000	573,000
Interest cost	215,000	295,000	429,000	590,000
Amortization of prior service cost	(176,000)	(144,000)	(224,000)	(289,000)
Net periodic benefit cost	$ 350,000	$ 437,000	$ 657,000	$ 874,000