Retirement Benefits (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4,011,000	$ 2,276,000
Interest cost	2,483,000	2,930,000
Expected return on plan assets	(5,197,000)	(5,016,000)
Amortization of net (income) loss	1,213,000	1,601,000
Settlement charge		104,000
Net periodic benefit cost	2,510,000	1,895,000
Pension contributions	0	0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	141,000	286,000
Interest cost	215,000	295,000
Amortization of prior service cost	(48,000)	(144,000)
Amortization of net (income) loss
Net periodic benefit cost	$ 308,000	$ 437,000