Income Taxes - Components of Net Deferred Income Tax Asset and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Net deferred income tax asset - Non-current
Warranty cost	$ 533	$ 695
Inventory reserve	1,559	419
Unearned service revenue	6,684	5,364
Employee stock options	4,222	4,366
Tax Credits	485	1,785
Loss carryforwards	7,038	8,782
Other, net	759	1,479
Deferred income tax asset - Non-current	21,280	22,890
Valuation Allowance	(1,924)	(1,631)
Net deferred income tax asset - Non-current	19,356	21,259
Bad debt reserve	(116)	(2)
Depreciation	(2,996)	(3,675)
Goodwill amortization	(1,612)	(1,574)
Intangible assets	(649)	(1,097)
Total deferred tax liabilities	(5,373)	(6,348)
Net deferred tax assets	$ 13,983	$ 14,911