Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income (loss)	$ (3,604)	$ 925
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Stock-based compensation	3,893	2,626
Depreciation of tangible assets	544	492
Amortization of contract acquisition costs	822
Change in deferred tax assets	(3,324)
Provision for doubtful accounts receivable	(487)	3
Other	(25)	(42)
Changes in assets and liabilities:
Accounts receivable	(1,832)	(1,641)
Inventories	(1,356)	(1,936)
Other current assets and prepaid expenses	(569)	(545)
Other long-term assets	(1,578)	(1)
Accounts payable	3,741	1,695
Accrued liabilities	(4,325)	1,534
Other long-term liabilities	70
Deferred revenue	546	784
Income tax liability	7	2
Net cash provided by (used in) operating activities	(6,503)	3,890
Cash flows from investing activities:
Acquisition of property, equipment and software	(581)	(210)
Disposal of property and equipment	38	40
Proceeds from sales of marketable investments	13,044	6,754
Proceeds from maturities of marketable investments	2,500	24,812
Purchase of marketable investments	(4,390)	(25,863)
Net cash provided by investing activities	10,611	5,533
Cash flows from financing activities:
Repurchase of common stock		(7,041)
Proceeds from exercise of stock options and employee stock purchase plan	3,038	3,871
Taxes paid related to net share settlement of equity awards	(2,664)	(1,167)
Payments on capital lease obligations	(234)	(182)
Net cash provided by (used) in financing activities	140	(4,519)
Net increase in cash and cash equivalents	4,248	4,904
Cash and cash equivalents at beginning of period	14,184	13,775
Cash and cash equivalents at end of period	18,432	18,679
Supplemental disclosure of non-cash items:
Assets acquired under capital lease	$ 533	$ 257