Accumulated Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Unrealized gains (losses)	$ (22,536)	$ 18,245
Amounts reclassified from accumulated other comprehensive income	(15,071)	4,684
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning balance	43,296	20,367
Ending balance	5,689	43,296
Derivative Instruments
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning balance	3,328	647
Unrealized gains (losses)	4,648	(4,359)
Amounts reclassified from accumulated other comprehensive income	(10,540)	7,040
Ending balance	(2,564)	3,328
Pension, Postretirement and Other Post-Employment Benefits
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning balance	40,311	19,720
Unrealized gains (losses)	(27,692)	22,923
Amounts reclassified from accumulated other comprehensive income	(4,346)	(2,332)
Ending balance	8,273	40,311
Available-for-Sale Securities
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning balance	(343)	0
Unrealized gains (losses)	508	(319)
Amounts reclassified from accumulated other comprehensive income	(185)	(24)
Ending balance	$ (20)	$ (343)