Income Taxes - Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income (loss) before income taxes
United States	$ 8,880	$ 12,708	$ (11,987)
Foreign	2,144	2,497	1,820
Income (loss) before income taxes	11,024	15,205	(10,167)
Current:
State	49	(33)	59
Foreign	(217)	374	780
Total current	(168)	341	839
Deferred:
Foreign	191	186	260
Total deferred	191	186	260
Income tax provision	23	527	1,099
Reconciliations of income taxes at the United States Federal statutory rate to the effective income tax rate
Income tax benefit at the United States statutory rate	3,859	5,322	(3,558)
State income taxes	32	(22)	38
Unrecognized tax benefits	(615)	(174)	184
Effect of change in valuation allowance	(7,765)	(5,676)	(6,835)
Foreign income tax rate differentials	233	600	259
Unremitted earnings of foreign subsidiaries	305	(102)	(758)
Stock options	264	379	686
Credit expirations	3,565
Deemed distribution from foreign subsidiaries			607
Discrete items, net		(540)	9,143
Other, net	145	740	1,333
Income tax provision	23	527	$ 1,099
Significant components of current deferred income taxes
Accrued compensation		1,082
Inventories		2,541
Warranty		1,214
Other		1,237
Deferred taxes, gross		6,074
Valuation allowance		(6,335)
Deferred taxes, net		(261)
Significant components of long-term deferred income taxes
Federal net operating loss carryforwards	98,007	101,479
State net operating loss carryforwards	1,546	1,636
Foreign net operating loss carryforwards	673	810
Federal tax credit carryforwards	12,778	16,343
State tax credit carryforwards	2,566	3,964
Unremitted earnings of foreign subsidiaries	(8,913)	(8,632)
Intangible assets	229	286
Property, plant and equipment	9,774	9,331
Accrued compensation	97
Inventories	5,230
Stock compensation	6,687	6,001
Warranty	930
Other	(5,578)	(3,945)
Deferred taxes, gross	124,026	127,273
Valuation allowance	(122,966)	(125,928)
Deferred taxes, net	$ 1,060	$ 1,345