Income Taxes - Summary of deferred tax liabilities (assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax liabilities:
Software development costs	$ 2,119	$ 2,223
Acquired intangible assets	913	1,731
Gross deferred tax liabilities	3,032	3,954
Allowances for bad debts and inventory	(2,958)	(4,505)
Capitalized inventory costs	(109)	(104)
Intangible assets	(672)	(1,388)
Employee benefit accruals	(1,282)	(2,089)
Federal net operating loss carryforward	(4,941)	(5,820)
State net operating loss carryforward	(1,540)	(1,085)
Tax credit carryforwards	(6,064)	(6,888)
Foreign currency	(33)	(33)
Other	(895)	(1,333)
Gross deferred tax assets	(18,494)	(23,245)
Less valuation allowance	1,653	1,874
Net deferred tax assets	$ (13,809)	$ (17,417)