Accumulated Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income (Loss)) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	$ 704,821
Unrealized gains	7,069
Amounts reclassified from AOCI	(3,577)
Ending Balance	697,950
Accumulated Other Comprehensive Income
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	43,296
Ending Balance	46,788
Derivative instruments
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	3,328
Unrealized gains	3,072
Amounts reclassified from AOCI	(3,133)
Ending Balance	3,267
Pension, postretirement and other post-employment benefits
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	40,311
Unrealized gains	3,331
Amounts reclassified from AOCI	(429)
Ending Balance	43,213
Available-for-sale securities
Accumulated Other Comprenhensive Income (Loss) [Roll Forward]
Beginning Balance	(343)
Unrealized gains	666
Amounts reclassified from AOCI	(15)
Ending Balance	$ 308