Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net loss	$ (14,603)	$ (14,894)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	692	485
Stock-based compensation expense	1,927	1,252
Amortization of premium on short-term investments	70	88
Interest accrued on long-term notes	37	0
Conversion of accrued interest to long-term debt	315	267
Changes in operating assets and liabilities:
Accounts receivable, net	4,198	1,966
Inventory	(2,379)	(2,690)
Prepaid expenses and other	758	(226)
Other assets	0	35
Accounts payable	270	1,097
Accrued liabilities	(4,610)	(3,747)
Deferred revenue	20,002	(663)
Deferred rent	904	310
Net cash provided by (used in) operating activities	7,581	(16,720)
Investing activities
Purchases of property and equipment	(828)	(632)
Proceeds from sale of short-term investments	1,250	3,000
Proceeds from maturity of short-term investments	11,200	22,679
Purchases of short-term investments	(12,450)	(11,900)
Net cash (used in) provided by investing activities	(828)	13,147
Financing activities
Repayment of lease financing obligations	(68)	(68)
Proceeds from issuance of common stock for employee stock purchase plan	767	664
Proceeds from exercise of stock options	269	82
Net cash provided by financing activities	968	678
Net increase (decrease) in cash and cash equivalents	7,721	(2,895)
Effect of exchange rate changes on cash and cash equivalents	10	20
Cash and cash equivalents
Beginning of period	21,856	17,223
End of period	$ 29,587	$ 14,348