Consolidated Statements of Cash Flows - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (136,314)	$ (95,765)	$ (70,275)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	7,143	6,176	5,535
Impairment of assets	576	2,138	1,557
Stock-based compensation	11,402	10,601	7,326
Inventory excess adjustments	502	2,110
Provision for doubtful accounts	143	984	529
Premium amortization and discount accretion on investment securities	857	1,445	288
Loss (gain) realized on investment securities	64	(191)
Loss (gain) on sales of property and equipment	12		(2)
(Gain) loss from changes in fair value of warrants	(1,148)	143	1,481
Interest accrued for borrowings	488	533
Amortization of debt discount	154		28
Gain from change in fair value of long term debt			(964)
Loss on debt extinguishment			7,313
Changes in operating assets and liabilities
Accounts receivable	5,001	(8,518)	(450)
Inventory	(3,086)	(431)	2,929
Prepaid expenses and other current assets	(1,515)	(2,077)	(3,797)
Restricted cash	1,033	150	(273)
Other assets	600	(2,812)	(1,041)
Accounts payable	217	1,256	1,354
Accrued compensation	(1,467)	2,515	2,572
Other accrued liabilities	14,919	(378)	8,026
Deferred revenue	846	430	32
Deferred rent, net of current portion	1,452	7,789
Other long-term liabilities	1,329
Net cash used in operating activities	(96,792)	(73,902)	(37,832)
Investing activities
Purchases of investments	(272,819)	(53,522)	(203,290)
Proceeds from sale of investments	65,270	59,185
Proceeds from maturity of investments	231,200	64,500
Proceeds from sale of property and equipment			463
Purchases of property and equipment, net	(9,867)	(23,136)	(7,852)
Net cash provided by (used in) investing activities	13,784	47,027	(210,679)
Financing activities
Proceeds from issuance of common stock, net of issuance costs			180,001
Proceeds from exercise of stock options	2,315	3,595	1,258
Proceeds from issuance of common stock under employee stock purchase plan	3,344	2,589
Proceeds from short-term financing			42,000
Borrowings under long-term debt facility	75,000
Payment for debt issuance costs on long-term debt facility	(287)
Borrowings under credit facility		8,000
Repayment under credit facility		(1,000)
Costs paid for loan			(6)
Repayments of equipment financing			(5,850)
Repayments of secured financings			(20,000)
Proceeds from collection of officer receivable			192
Payment to lender for debt extinguishment			(7,313)
Net cash provided by financing activities	80,372	13,184	190,282
Net decrease in cash	(2,636)	(13,691)	(58,229)
Cash at beginning of period	15,256	28,947	87,176
Cash at end of period	12,620	15,256	28,947
Supplemental disclosure of cash flow information:
Cash paid for income taxes	177
Cash paid for interest	3,568		2,060
Non-cash investing and financing activities:
Purchases of property and equipment through accounts payable and accruals	$ 447	$ 5,204	765
Issuance of common stock for lender's commitment to debt financing	2,448
Conversion of convertible preferred stock to common stock			$ 240,585