Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net loss	$ (13,938)	$ (16,592)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,801	3,797
Change in lease-related performance liabilities	(623)	(572)
Stock-based compensation expense	12,207	11,653
Amortization of debt discount and issuance costs	3,504	3,219
Other	1,325	151
Changes in operating assets and liabilities:
Accounts receivable	14,293	10,425
Other receivables	(275)	(1,468)
Inventories	(3,866)	(834)
Prepaid expenses and other assets	(607)	(541)
Deferred commissions	(640)	385
Accounts payable	(1,035)	(841)
Increase (Decrease) in Other Accrued Liabilities	1,176	(2,674)
Deferred revenue	(7,461)	(6,027)
Net cash used in operating activities	6,861	81
Cash flows from investing activities
Purchase of property and equipment	(1,427)	(1,778)
Purchase of short-term investments	(86,300)	(43,384)
Maturities of short-term investments	72,137	61,228
Sales of short-term investments	14,393	0
Net cash used in investing activities	(1,197)	16,066
Cash flows from financing activities
Cash from lease-related performance obligations	306	645
Payment for purchase of capped calls	(8,907)
Proceeds from issuance of common stock from the employee stock purchase plan	1,966	1,809
Proceeds from exercise of stock options	1,325	2,091
Tax withholdings paid on behalf of employees for net share settlement	(5,579)	(10,067)
Net cash provided by financing activities	(1,982)	(5,522)
Net increase in cash and cash equivalents	3,682	10,625
Cash and cash equivalents at beginning of period	25,704	34,276
Cash and cash equivalents at end of period	29,386
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment in accounts payable and accrued liabilities	$ 222	$ 117