Income Taxes - Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (decrease) in income taxes resulting from:
Income tax benefit at Federal statutory income tax rate	$ (1,611)	$ (3,379)	$ (670)
State income tax expense, net of federal benefit	172	56	(156)
State research and development, investment credits	(397)	(435)	(363)
Non-deductible meals & entertainment	28	47	49
Non-deductible stock compensation expense	21	338	216
Non-deductible transaction costs	0	0	116
Subpart F income, net of foreign tax credits	0	1,171	523
GILTI	577	0	0
Foreign branch income	0	0	52
Nontaxable interest income	2	0	(162)
Foreign tax rate differential	(93)	(902)	(1,258)
Federal research and development credits	(378)	(427)	(395)
Uncertain tax positions	(209)	189	283
Provision to tax return adjustments	470	8	(95)
Change in tax rates	(3)	926	14
Change in valuation allowance	2,130	3,330	7,425
Foreign research and development incentives	(32)	(22)	(45)
Other	(112)	196	13
Income tax expense	$ 565	$ 1,096	$ 5,547