Accumulated Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	$ 704,821
Unrealized gains	6,184
Amounts reclassified from AOCI	(9,169)
Ending Balance	705,436
Accumulated Other Comprehensive Income
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	43,296
Ending Balance	40,311
Derivative instruments
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	3,328
Unrealized gains	3,836
Amounts reclassified from AOCI	(6,257)
Ending Balance	907
Pension, postretirement and other post-employment benefits
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	40,311
Unrealized gains	1,745
Amounts reclassified from AOCI	(2,862)
Ending Balance	39,194
Available-for-sale securities
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	(343)
Unrealized gains	603
Amounts reclassified from AOCI	(50)
Ending Balance	$ 210