Income Taxes - Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income (loss) before income taxes
United States	$ 51,934	$ 18,148	$ 52,172
Foreign	3,952	2,774	2,533
Income before income taxes	55,886	20,922	54,705
Current:
Federal			41
State	157	5	112
Foreign	1,062	579	323
Total current	1,219	584	476
Deferred:
Federal	4,594	3,962	8,108
State	295	(855)	425
Foreign	(204)	197	(189)
Total deferred	4,685	3,304	8,344
Income tax provision	5,904	3,888	8,820
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	11,736	4,393	11,488
State income taxes	226	78	299
Unrecognized tax benefits		(251)	(345)
Effect of change in valuation allowance	806	1,492	(441)
Foreign income tax rate differentials	181	129	73
Stock based compensation	(2,803)	(1,257)	(715)
Credit expirations	(14)	894
Rate change	151	194	160
Credit generation	(2,473)	(3,124)	(3,530)
Discrete items, net	(147)	18	972
Previously unrecognized tax benefit	(4,063)
GILTI inclusion	732	566	366
Other, net	1,572	756	493
Income tax provision	5,904	3,888	$ 8,820
Deferred tax assets:
Federal net operating loss carryforwards	23,193	39,380
State net operating loss carryforwards	969	1,211
Foreign net operating loss carryforwards	529	554
Federal tax credit carryforwards	19,377	18,061
State tax credit carryforwards	7,358	6,837
Property, plant and equipment	9,501	10,098
Operating lease liability	348	503
Accrued compensation	16	266
Inventories	2,271	2,674
Stock compensation	1,566	2,477
Warranty	982	689
Deferred revenue	1,032	1,086
Capitalized research and development costs	5,785
Gross deferred tax assets	72,927	83,836
Valuation allowance	(9,133)	(8,327)
Net deferred tax assets	63,794	75,509
Deferred tax liabilities:
Intangible assets	(80)	(47)
Right-of-use asset	(4,756)	(5,141)
Internal Revenue Code 481(a) adjustment		(412)
Other	(1,107)	(1,849)
Gross deferred tax liabilities	(5,943)	(7,449)
Deferred taxes, net	$ 57,851	$ 68,060