Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (10,260)	$ (4,477)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	7,004	5,524
Depreciation of tangible assets	1,184	849
Amortization of contract acquisition costs	2,169	1,304
Change in deferred tax asset	(2)	(3,507)
Provision for doubtful accounts receivable	(647)	(877)
Other	55	215
Changes in assets and liabilities:
Accounts receivable	(4,232)	(5,544)
Inventories	(6,028)	(2,540)
Other current assets and prepaid expenses	(1,423)	(797)
Other long-term assets	(2,608)	(2,301)
Accounts payable	2,861	6,319
Accrued liabilities	4,900	(4,177)
Extended warranty liabilities	(927)
Other long-term liabilities	(140)	105
Deferred revenue	907	58
Income tax liabilities	(301)	(27)
Net cash used in operating activities	(6,194)	(8,119)
Cash flows from investing activities:
Acquisition of property, equipment and software	(524)	(1,214)
Disposal of property and equipment	45	41
Proceeds from sales of marketable investments		13,044
Proceeds from maturities of marketable investments	11,450	8,050
Purchase of marketable investments	(8,304)	(4,390)
Net cash provided by investing activities	2,667	15,531
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	1,600	3,603
Taxes paid related to net share settlement of equity awards	(750)	(2,971)
Payments on finance lease obligations	(496)	(362)
Net cash provided by financing activities	354	270
Net increase (decrease) in cash and cash equivalents	(3,173)	7,682
Cash and cash equivalents at beginning of period	26,052	14,184
Cash and cash equivalents at end of period	22,879	21,866
Supplemental disclosure of non-cash items:
Assets acquired under finance lease	$ 903	$ 610