Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities
Net loss	$ (90,812)	$ (57,858)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,320	4,177
Stock-based compensation	8,406	7,965
Premium amortization and discount accretion on investment securities	703	1,145
Amortization of debt discount	51
Inventory excess adjustments	413
Loss on disposal of property and equipment	12
Impairment of assets	576	407
Non-cash interest accrual	1,825	383
Loss (gain) on investments	55	(192)
Loss (gain) from changes in fair value of warrants	397	(91)
Provision for doubtful accounts	(93)	354
Changes in operating assets and liabilities
Accounts receivable	6,147	(3,900)
Inventory	(3,187)	(1,156)
Prepaid expenses and other current assets	660	(4,057)
Restricted cash	1,047	54
Other assets	476	(3,028)
Accounts payable	(4,548)	1,653
Accrued compensation	(1,639)	1,662
Other accrued liabilities	3,724	1,552
Deferred revenue	467	432
Deferred rent, net of current portion	1,351	6,092
Net cash used in operating activities	(68,649)	(44,406)
Investing Activities
Purchases of investments	(184,263)	(48,519)
Proceeds from sale of investments	55,352	59,185
Proceeds from maturity of investments	124,325	34,000
Purchases of property and equipment, net	(9,147)	(14,577)
Net cash (used in) provided by investing activities	(13,733)	30,089
Financing Activities
Proceeds from exercise of stock options	1,834	2,722
Proceeds from issuance of common stock under employee stock purchase plan	1,503	970
Borrowings under long-term debt facility	75,000
Borrowings under credit facility		8,000
Repayment under credit facility		(1,000)
Net cash provided by financing activities	78,337	10,692
Net decrease in cash	(4,045)	(3,625)
Cash at beginning of period	15,256	28,947
Cash at end of period	$ 11,211	$ 25,322