INCOME TAXES - Tax Effects and Tax Cuts and Jobs Act (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of components of income before income taxes
Domestic	$ 8,478	$ 17,188	$ 10,894
Foreign	10,298	6,653	9,787
Income before income taxes	18,776	23,841	20,681
Current provision
Domestic	2,167	4,313	1,663
Foreign	3,485	2,618	3,169
Total current provision	5,652	6,931	4,832
Deferred provision
Domestic	288	199	675
Foreign	(807)	(311)	(751)
Total deferred provision	(519)	(112)	(76)
Provision for income taxes	$ 5,133	$ 6,819	$ 4,756
Differences in the provision for income taxes from the amount determined by applying the federal statutory rate
Tax provision, computed at statutory rate (as a percent)	21.00%	21.00%	21.00%
State tax, net of federal impact (as a percent)	4.20%	4.50%	3.00%
Change in valuation allowance (as a percent)	0.00%	0.30%	2.80%
Effect of foreign tax rate differences (as a percent)	4.30%	1.50%	3.40%
Permanent items, other (as a percent)	(0.20%)	1.40%	0.80%
Section 162(m) compensation	2.20%	1.10%	0.10%
R&D Credit (as a percent)	(3.60%)	(2.50%)	(0.80%)
Restricted stock awards (as a percent)	0.60%	(0.10%)	(2.30%)
Effect of Tax Cuts and Jobs Act (as a percent)	(1.30%)	(0.40%)	(5.10%)
Subpart F income (as a percent)	1.30%	0.00%	0.00%
Tax examinations (as a percent)	0.00%	1.80%	0.00%
Other (as a percent)	(1.20%)	0.00%	0.10%
Provision for income taxes (as a percent)	27.30%	28.60%	23.00%
US federal corporate tax rate (as a percent)	21.00%	21.00%	21.00%
Noncurrent deferred tax assets:
Employee benefit plans	$ 2,500	$ 2,440
Net operating loss and tax credit carryforwards	2,217	1,675
Accrued expenses and reserves	969	795
Other	697	428
Total noncurrent deferred tax assets	6,383	5,338
Valuation allowance	(1,176)	(1,077)
Net noncurrent deferred tax assets:	5,207	4,261
Net noncurrent deferred tax liabilities:
Property and equipment	3,448	3,901
Goodwill and intangibles	5,629	2,885
Other	459	384
Total deferred tax liabilities	9,536	7,170
Foreign tax credits	900
Tax effect on net operating losses	200
Noncurrent deferred income tax assets	330	490
Noncurrent deferred income tax assets	(4,659)	(3,399)
Net deferred tax asset/(deferred tax liability)	(4,329)	(2,909)
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries	275
Unrecognized Tax Benefits	0	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	0	$ 0	$ 0
Domestic Tax Authority [Member]
Net noncurrent deferred tax liabilities:
Operating Loss Carryforwards	4,139
Domestic Tax Authority [Member] | Foreign Tax Credit [Member]
Net noncurrent deferred tax liabilities:
Tax Credit Carryforward, Amount	1,003
Foreign
Net noncurrent deferred tax liabilities:
Operating Loss Carryforwards	1,519
Operating Loss Carryforwards, Unlimited Carryforward	718
Foreign | R&D Tax Credits
Net noncurrent deferred tax liabilities:
Tax Credit Carryforward, Amount	$ 574