Income Taxes - Summary of deferred tax liabilities (assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax (liabilities) assets:
Software development costs	$ (1,954)	$ (2,119)
Acquired intangible assets	(676)	(913)
Gross deferred tax liabilities	(2,630)	(3,032)
Allowances for bad debts and inventory	2,785	2,958
Capitalized inventory costs	116	109
Intangible assets	420	672
Employee benefit accruals	1,742	1,282
Federal net operating loss carryforward	6,512	4,941
State net operating loss carryforward	2,112	1,540
Tax credit carryforwards	6,176	6,064
Foreign currency	0	33
Depreciation on property, plant and equipment	373	168
Other	722	727
Gross deferred tax assets	20,958	18,494
Less valuation allowance	(18,328)	(1,653)
Net deferred tax assets	$ 0	$ 13,809