Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (23,407)	$ (25,408)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	1,661	1,451
Stock-based compensation expense	5,109	4,309
Amortization of premium on short-term investments	78	73
Interest accrued on long-term debt	85	74
Conversion of accrued interest to long-term debt	724	632
Bad debt expense	201	0
Changes in operating assets and liabilities:
Accounts receivable, net	3,515	(5,516)
Inventory	(2,472)	(3,283)
Prepaid expenses and other	(1,506)	260
Other assets	(87)	(89)
Accounts payable	(392)	660
Accrued liabilities	(488)	(2,832)
Deferred revenue	(13,307)	32,314
Deferred rent and other liabilities	1,320	1,675
Net cash (used in) provided by operating activities	(28,966)	4,320
Investing activities
Purchases of property and equipment	(3,384)	(2,231)
Proceeds from sale of short-term investments	1,000	1,250
Proceeds from maturity of short-term investments	28,474	16,700
Purchases of short-term investments	(34,785)	(28,625)
Net cash used in investing activities	(8,695)	(12,906)
Financing activities
Borrowings under long-term debt agreement	0	5,000
Repayment of lease financing obligations	(58)	(135)
Proceeds from sale of common stock, net	56,486	0
Tax withholdings related to net share settlements of restricted stock units	(248)	0
Proceeds from issuance of common stock for employee stock purchase plan	926	767
Proceeds from exercise of stock options	601	395
Net cash provided by financing activities	57,707	6,027
Net (decrease) increase in cash and cash equivalents	20,046	(2,559)
Effect of exchange rate changes on cash and cash equivalents	18	(3)
Cash and cash equivalents
Beginning of period	20,583	21,856
End of period	$ 40,647	$ 19,294