Pension Benefits and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits
Change in benefit obligation:
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	1,785	1,692	3,569	3,372
Expected return of plan assets	(2,192)	(2,164)	(4,384)	(4,333)
Amortization of prior service credit	0	0	0	0
Amortization of net loss	456	457	910	913
Net periodic cost (benefit)	49	(15)	95	(48)
Retirement Health and Life Insurance Benefits
Change in benefit obligation:
Service cost	18	17	36	38
Interest cost	15	16	30	31
Expected return of plan assets	0	0	0	0
Amortization of prior service credit	(253)	(400)	(506)	(801)
Amortization of net loss	0	0	0	0
Net periodic cost (benefit)	$ (220)	$ (367)	$ (440)	$ (732)