Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities
Net loss	$ (34,091)	$ (32,873)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,920	1,860
Non-cash lease expense	1,890
Stock-based compensation	4,051	3,154
Premium amortization and discount accretion on investment securities	70	144
Amortization of debt discount	98	98
Inventory excess adjustments	101	45
Impairment of assets		1,544
Loss on investments		32
Loss from changes in fair value of warrants		108
Other non-cash charges	8	61
Changes in operating assets and liabilities
Accounts receivable	2,145	(6,284)
Inventory	(216)	(2,959)
Prepaid expenses and other current assets	(2,135)	2,524
Other assets	201	215
Accounts payable	(5,466)	51
Accrued compensation	(1,850)	333
Other accrued liabilities	1,018	(2,799)
Deferred revenue	437	35,485
Deferred rent, net of current portion		307
Net cash (used in) provided by operating activities	(31,819)	1,046
Investing activities
Purchases of investments	(18,628)	(9,985)
Proceeds from sale of investments		27,896
Proceeds from maturity of investments	32,500	8,000
Purchases of property and equipment, net	(955)	(852)
Net cash provided by investing activities	12,917	25,059
Financing activities
Proceeds from exercise of stock options	2,578	564
Net cash provided by financing activities	2,578	564
Net (decrease) increase in cash, cash equivalents and restricted cash	(16,324)	26,669
Cash, cash equivalents and restricted cash, beginning of period	51,004	13,021
Cash, cash equivalents and restricted cash, end of period	34,680	39,690
Supplemental non-cash investing and financing activities:
Obtaining right-of-use assets in exchange for lease liabilities	28,191
Purchases of property and equipment in accounts payable and accruals	$ 199	$ 209