Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Accrued expenses and allowances	$ 22,912	$ 19,731
Inventories	5,670	5,599
Net operating loss carryforwards	25,089	27,541
Other	7,077	8,020
Subtotal	60,748	60,891
Less: valuation allowance	(805)	(21,958)
Total net deferred tax assets	59,943	38,933
Deferred tax liabilities
Property, plant and equipment	(538,746)	(487,634)
Intangible Assets	(51,835)	(33,322)
Other	(5,651)	(2,146)
Total deferred tax liabilities	(596,232)	(523,102)
Net deferred tax liability	$ (536,289)	$ (484,169)