L. INCOME TAXES - NARRATIVE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation allowance increase (decrease)			$ 1,700	$ 13,100
Valuation allowance				1,663
Net operating loss carryforward	$ 37,700		$ 37,700
Loss carryforward expiration date			Dec. 31, 2032
Foreign tax credit	2,018		$ 2,018
Research and development tax credits	4,600		$ 4,600
Research and development tax credit expiration date			Dec. 31, 2037
Federal income tax rate			35.00%
China income tax rate			25.00%
Reduction in income tax provision due to tax holiday			$ 1,400
Increase in diluted earnings per share due to tax holiday			$ 0.07
Unrecognized tax benefits	181		$ 181	1,797	$ 1,797	$ 1,659
Accrued penalties or interest				$ 0
Impact on change in tax rate			2,800
Impact on deferred tax assets due to change in tax rate			2,800
Repatriation tax			5,000
Income tax			9,000
Foreign tax credits			4,000
Reduction to net deferred tax assets attributable to accelerated depreciation	700
Forecast
Federal income tax rate		21.00%
ASU 2016-09
Deferred tax asset, changes in accounting standard	1,200		1,200
Credit to retained earnings	1,200		$ 1,200
Foreign tax credits
Loss carryforward expiration date			Dec. 31, 2037
Foreign tax credit	$ 2,000		$ 2,000
Global [Member]
China income tax rate			15.00%
Tax rate effective period			3 years
Extended period of tax preferential status			3 years