Income Taxes Deferred Tax Assets Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carry-forwards	$ 6,300	$ 7,976
Tax credit carry-forwards	1,154	1,002
Accruals for compensation	7,160	9,399
Accruals for inventory capitalization	1,813	1,909
Unrealized benefit plan loss	3,417	4,006
Unrealized foreign exchange	7,542	5,932
Unearned revenue	2,760	2,649
Other	822	580
Total deferred tax assets	30,968	33,453
Valuation allowance	(9,732)	(8,219)	$ (10,000)
Net deferred tax assets	21,236	25,234
Deferred tax liabilities:
Intangibles	(6,025)	(5,939)
Property, plant and equipment	(2,835)	(2,968)
Accrued interest	(3,260)	(4,885)
Accruals for compensation	0	(1,501)
Accrued withholding taxes	(886)	(2,191)
Unrealized foreign exchange	(4,043)	(1,995)
Other	(569)	(359)
Total deferred tax liabilities	17,618	19,838
Total deferred tax assets (liabilities)	3,618	5,396
Long-term deferred tax assets	11,252	10,719
Long-term deferred tax liabilities	$ (7,634)	$ (5,323)