Retirement Benefits (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,276,000	$ 2,977,000	$ 4,553,000	$ 5,954,000
Interest cost	2,930,000	2,585,000	5,860,000	5,170,000
Expected return on plan assets	(5,016,000)	(3,670,000)	(10,031,000)	(7,341,000)
Amortization of net (income) loss	1,601,000	2,237,000	3,203,000	4,473,000
FAS 88 settlement charge	104,000		208,000
Net periodic benefit cost	1,895,000	4,129,000	3,793,000	8,256,000
Pension contributions	0	0	0	0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	286,000	446,000	573,000	893,000
Interest cost	295,000	307,000	590,000	614,000
Amortization of prior service cost	(144,000)	(33,000)	(289,000)	(66,000)
Amortization of net (income) loss		94,000		188,000
Net periodic benefit cost	$ 437,000	$ 814,000	$ 874,000	$ 1,629,000