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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	1,692	1,837	5,064	5,519
Expected return of plan assets	2,164	2,302	6,497	6,920
Amortization of prior service credit	0	0	0	0
Amortization of net loss (gain)	(457)	(445)	(1,370)	(1,311)
Net periodic (benefit) cost	(15)	(20)	(63)	(90)
Retirement Health and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	17	12	55	68
Interest cost	16	20	47	51
Expected return of plan assets	0	0	0	0
Amortization of prior service credit	(400)	(411)	(1,201)	(1,191)
Amortization of net loss (gain)	0	(16)	0	15
Net periodic (benefit) cost	$ (367)	$ (363)	$ (1,099)	$ (1,087)