Pension Benefits and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Change in benefit obligation:
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	1,790	1,692	5,359	5,064
Expected return of plan assets	(2,187)	(2,164)	(6,571)	(6,497)
Amortization of prior service credit	0	0	0	0
Amortization of net loss	476	457	1,386	1,370
Net periodic cost (benefit)	79	(15)	174	(63)
Retirement Health and Life Insurance Benefits
Change in benefit obligation:
Service cost	12	17	48	55
Interest cost	14	16	44	47
Expected return of plan assets	0	0	0	0
Amortization of prior service credit	(252)	(400)	(758)	(1,201)
Amortization of net loss	0	0	0	0
Net periodic cost (benefit)	$ (226)	$ (367)	$ (666)	$ (1,099)