Pension Benefits and Other Postretirement Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits
Change in benefit obligation:
Service cost	$ 0	$ 0
Interest cost	1,784	1,680
Expected return of plan assets	(2,192)	(2,169)
Amortization of prior service credit	0	0
Amortization of net loss	454	456
Net periodic cost (benefit)	46	(33)
Retirement Health and Life Insurance Benefits
Change in benefit obligation:
Service cost	18	20
Interest cost	15	15
Expected return of plan assets	0	0
Amortization of prior service credit	(253)	(400)
Amortization of net loss	0	0
Net periodic cost (benefit)	$ (220)	$ (365)