Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities
Net loss	$ (63,693)	$ (31,841)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,620	2,428
Stock-based compensation	5,420	5,292
Premium amortization and discount accretion on investment securities	515	761
Inventory excess adjustments	187
Loss on disposal of property and equipment	12
Impairment of assets	576	20
Non-cash interest accrual	399	237
Loss (gain) on investments	47	(112)
(Gain) loss from changes in fair value of warrants	(320)	306
Provision for doubtful accounts	(240)	479
Changes in operating assets and liabilities
Accounts receivable	6,530	(789)
Inventory	(1,132)	(800)
Prepaid expenses and other current assets	1,349	(296)
Restricted cash	328	(32)
Other assets	223	(532)
Accounts payable	2,028	2,150
Accrued compensation	(2,961)	543
Other accrued liabilities	7,493	(156)
Deferred revenue	96	188
Deferred rent, net of current portion	1,457	1,964
Net cash used in operating activities	(38,066)	(20,190)
Investing Activities
Purchases of investments	(4,219)	(30,118)
Proceeds from sale of investments	36,791	16,766
Proceeds from maturity of investments	3,000	18,000
Proceeds from sale of property and equipment		225
Purchases of property and equipment, net	(8,066)	(7,311)
Net cash provided by (used in) investing activities	27,506	(2,438)
Financing Activities
Proceeds from exercise of stock options	939	2,268
Proceeds from issuance of common stock under employee stock purchase plan	1,503	970
Borrowings under credit facility		8,000
Repayment under credit facility		(1,000)
Net cash provided by financing activities	2,442	10,238
Net decrease in cash	(8,118)	(12,390)
Cash at beginning of period	15,256	28,947
Cash at end of period	$ 7,138	$ 16,557