Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Foreign tax credit carryforwards	$ 20,360	$ 19,836
Net operating loss carryforwards	54,772	50,737
Employee benefits	10,778	12,583
Inventory	7,725	6,065
Other	4,686	4,488
Gross deferred tax asset	98,321	93,709
Valuation allowance	(35,828)	(33,762)
Net deferred tax asset	62,493	59,947
Deferred tax liabilities:
Tax over book depreciation	(36,387)	(46,942)
Intangible assets	(56,867)	(57,867)
Convertible senior notes discount	(4,964)	(6,569)
Other	(1,669)	(1,639)
Deferred tax liability	(99,887)	(113,017)
Net deferred tax liability	$ (37,394)	$ (53,070)