Income Taxes - Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income (loss) before income taxes
United States	$ 18,148	$ 52,172	$ 40,752
Foreign	2,774	2,533	3,079
Income before income taxes	20,922	54,705	43,831
Current:
Federal		41	430
State	5	112	32
Foreign	579	323	230
Total current	584	476	692
Deferred:
Federal	3,962	8,108	(82,048)
State	(855)	425	(1,698)
Foreign	197	(189)	(74)
Total deferred	3,304	8,344	(83,820)
Income tax provision (benefit)	3,888	8,820	(83,128)
Reconciliation of income taxes at the United States Federal statutory rate to the effective income tax rate
Income taxes at the United States statutory rate	4,393	11,488	15,341
State income taxes	78	299	203
Unrecognized tax benefits	(251)	(345)	(285)
Effect of change in valuation allowance	1,492	(441)	(115,831)
Foreign income tax rate differentials	129	73	(312)
Unremitted earnings of foreign subsidiaries			(8,933)
Stock options	(1,257)	(715)	(10,342)
Credit expirations	894
Repatriation of foreign earnings			4,556
Recognition of equity NOL's			(1,165)
Rate change	194	160	42,531
Credit generation	(3,124)	(3,530)	(8,778)
Discrete items, net	18	972	31
Other, net	1,322	859	(144)
Income tax provision (benefit)	3,888	8,820	$ (83,128)
Deferred tax assets:
Federal net operating loss carryforwards	39,380	42,397
State net operating loss carryforwards	1,211	1,387
Foreign net operating loss carryforwards	554	641
Federal tax credit carryforwards	18,061	16,200
State tax credit carryforwards	6,837	6,489
Property, plant and equipment	10,098	5,924
Operating lease liability	503
Accrued compensation	266	97
Inventories	2,674	3,713
Stock compensation	2,477	2,760
Warranty	689	1,090
Deferred revenue	1,086	1,004
Gross deferred tax assets	83,836	81,702
Valuation allowance	(8,327)	(6,835)
Net deferred tax assets	75,509	74,867
Deferred tax liabilities:
Intangible assets	(47)	(29)
Right-of-use asset	(5,141)
Internal Revenue Code 481(a) adjustment	(412)
Other	(1,849)	(2,899)
Gross deferred tax liabilities	(7,449)	(2,928)
Deferred taxes, net	$ 68,060	$ 71,939